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VTX 1300 Carburetor Adjustment

326K views 547 replies 188 participants last post by  Timbanditos 
#1 · (Edited by Moderator)
You may have just purchased a new exhaust and/or air intake and are wondering how you should "tune" the carburetor. First off if you just "fire the bike up" with the new parts installed, THE BIKE WILL RUN. Depending on how "free flowing" the aftermarket parts are that you installed the bike will run anywhere from "pretty good" to "pretty lean and very nervous", but it will run. So now the bike has to be TUNED. The easiest, least expensive, quickest, most predictable and fool proof method of rapidly tuning it would be to ADJUST the stock parts that are already in the carb. Some people venturing into the "mods" game want to do them all at the same time... this has OFTEN been proven to cause problems for the neuvo MC "wrench". DO NOT remove the PAIR system during the same session that you are tuning the carb. :nono: , it is common while working with the PAIR removal to "miss" something in the process and have an open vacuum line or "other" air leak. Many who have done both of these mods simultaneously have ended up fiddling with their carb for days/weeks on end chasing their tails looking for what went wrong with the carb tuning while all the time it was an error in the PAIR system removal. There have been some war stories spread about how difficult it is to tune a carburetor.. bull hocky! The most difficult part of tuning a carb on a VTX 1300 is removing the fuel tank for the first time and figuring out how to disconnect the electrical connectors under the tank.

So, what comes first eh? REMOVE THE FUEL TANK. Follow the directions in the service manual.. everyone should have a service manual.. the money you save in THIS carb tuning process alone will pay for a service manual. The money you save doing your first valve adjust using the service manual would buy a nice set of tools that can be used in OTHER money savings projects... EVERYONE needs a service manual..

Next REMOVE the air filter and backing plate. I won't "get into" hooking and unhooking the hoses attached behind the backing plate, they are pretty straight forward and will become part of your "learning process" of the easiest ways to rapidly navigate through assembly/disassembly.

NOW the carburetor is EXPOSED. Sitting on top of the carb you will see the vacuum chamber cover. Remove the cover and then remove the compression spring under the cover. Now gently grab the diaphragm/piston rubber and pull it out.. the Vacuum piston (slider piston is what most old timers call it) is attached to the diaphram and the whole package will come out with it. YOU ARE ALMOST DONE AND READY TO PUT THINGS BACK TOGETHER.. see, I told you.. removing the tank was the most difficult part of the process... unscrewing the 4 vacuum chamber cover screws was no big deal, right?
Look at the slider piston and you will see a tappered "needle" sticking out the bottom of it, that is the jet needle. Look inside the slider piston and you will see the Jet needle holder. The jet needle holder is next to be removed.. you will see in the center of the holder it will accept a Phillips head screwdriver which can be used to "unscrew" the cam locks, BUT the "best" method is to use a small socket and fit over the head of the "cap" and unscrew the cap... I'm thinking it's an 8mm.. difficult to recall those things sometimes at my age, but you'll discover the correct size. Twist the cap counter clockwise just as tho you were unscrewing any "standard" nut or bolt and you will feel a "pop" after making a very small motion.. that was the cams unlocking.. the cap can now be removed, it is "unlocked".

Under the needle holder cap there is a small spring "screwed" onto a plastic "tit" protruding from the bottom of the cap... well actually the "tit" has no threads, so the spring is not "screwed" on, but consider it so... instead of "pulling" the spring off and distorting it's shape, give a "light force" pull on the spring while unscrewing it from the "tit" and set the spring aside. The "tit" does not protrude very far, but it must be "trimmed" for "heavy breather" mods, so go ahead and trim it now even if you are doing a "light breather" tune... Take some TOENAIL clippers (those are the large ones, not to be confused with fingernail clippers) and "snip" the "tit" in half.. that should be enough for heightened needle raising and still provides enough remaining "tit" for the small spring to be screwed back onto... set the needle holder cap aside.

Remove the needle from the slider piston.. place your shims into the needle "point" and make sure they slide all the way to the needle head with the washer/shim hole big enough so free movement along the needle is achieved. Hold the slider piston in your left hand and turn it at an upwards angle and insert the needle INTO the slider piston hole, passing through the CENTER hole in the slider piston (this process will not work for "left handers", you will have to purchase a Yamaha carburetor). Face the slider piston DOWN and the needle should be hanging from the bottom of the slider piston and sitting "on" the shims/washers INSIDE the piston.

Take the SMALL spring that was unscrewed from the underside of the needle holder cap and screw it back onto the shortened "tit" under the needle holder. Put the needle holder cap into the slider piston with the small needle spring tensioner sitting on top of the needle head. (If the 8mm socket is placed onto the top of the needle holder cap "nut" the tension is enough to hold the cap.. the needle cap holder can be easily inserted into the slider piston with this method utilizing a socket extender). Twist the needle holder cap clockwise (even the left handers) as tho "tightening" and you will feel the cams lock into place... that's it, the needle holder is locked. If enough of the "tit" was trimmed, this should be a relatively easy "twist"... Hold the slider piston with one hand and "wiggle" the needle with the fingers on the other hand... the needle should "wiggle" (movement), this assures true alignment into the emulsion tube :) . If the needle is "stiff" and won't "wiggle", then the "tit" was not trimmed enough :nono: ... go back and trim more from the tit until free needle movement is achieved. (If you are using a DJ needle, the tit must also be trimmed for the same reasons)

Replace the diaphragm spring onto the needle holder cap and replace the vacuum chamber cover.. NOTE: There is an irregular "shape" in the cap that must be matched to it's mating surface when remounting, this is what the manual calls the "tab and air passages"... "Snug" the vacuum cap screws and continue reassembly.

Under the carb is the A/F screw (see manual), the stock screw head requires a "D" type tool for adjustment. If you slightly dent the end of an empty .22 shell casing, this will fit into the hole and can be used to unscrew the "D" screw. Take the "D" screw completely OUT. On the top of the "D" screw head will be a spring followed by a washer and then an "O" ring.. save these parts and reassemble in the same order when putting the A/F screw back in.

While the A/F screw is OUT, use a hacksaw blade or some similar device to cut a thin channel into the head of the top of the "D" screw.. this slot or channel should be wide enough for a flathead screwdriver blade to fit into for A/F adjustment. Once the slot has be cut into the screw/needle head and the screwdriver blade fits, replace the spring/washer and "O" ring and replace the A/F needle into the needle jet hole and screw IN. Take your screw driver and screw in the needle until it LIGHTLY seats or stops turning ;) ... don't get anal about this and over tighten or damage could be caused to the needle/jet mating surfaces :( . If you error on "seating", error on the LOOSE side, final tuning will not be affected by a minute discrepancy of "seating" at this stage of tuning. Turn the A/F screw OUT 2 1/2 turns with the screwdriver.

Reassemble the airbox and fuel tank.

Before firing the engine, look at the CHOKE KNOB and push it in all the way... any flexing of the carb while working on it will flex the choke cable and pull the choke out... it will not run properly with the choke pulled out AT ALL and final tuning cannot be achieved.

Shim heights:
"Open" style airbox and aftermarket "free flow" pipes... usually about 2or 3 shims.
Airbox flowing more air than stock design, but not in the "heavy breathing" class and/or pipes either free flow or somewhat restricted... usually about 1or 2 shims
Stock airbox (K&N filter in stock box is still "stock") and after market pipes... usually 0 or 1 shims
Stock airbox and stock pipes... tune the A/F screw for maximum performance...

A/F settings:
While determining proper main jet circuit settings the A/F screw should be set at 2 1/2 turns and NO adjustments made to it until the high speed circuit has been properly tuned -- Turning the screw IN leans the mixture... turning the screw OUT richens the mixture -- Fine tuning the A/F screw should be done in no more than 1/8 turn increments... very fine tuning will be even less... it is highly recommended to "slot" the "D" screw and tune the A/F screw with a screw driver... a 90 degree drive is useful if you have one... improvise.

SLIDER PISTON SPRING:
That's what I call the big spring directly under the vacuum cap and sitting on the needle holder cap. -- Most tuners that have springs of the type found in the VTX carb shorten the spring for faster throttle response... this is not necessary for the bike to operate, but you will shorten the response time if you shorten it... I would not recommend shortening it past 5 1/16"... that is the lenght of the shorter DJ kit supplied spring and is a proven entity... The Keihin spring is of slightly larger diameter wire so a "safe" fudge factor is built in if you cut it to 5 1/16", most do... you can cut it less than that if you are nervous, but you shouldn't have any problems with 5 1/16"... place the cut end DOWN into the slider piston and resting on the needle cap... uncut end UP against the vacuum cover.. that is the "common" practice (and no bannanas on boats either).

Most any needle design or jet design will work with the Keihin carb as long as they are set to the proper height and have the correct diameter... It has been my findings that the stock Keihin needle and jet work more "smoothly" if properly shimmed than some other designs because of the needle design and large diameter jet size... The Keihin design is just more forgiving and not as "touchy" as some other designs and need I say you are not required to remove the float bowl cover to change main jet sizes?... The Keihin 195 main jet suits most all purposes... if you require more than that you are past the "beginning" tuner stages and in that case you might think about a Keihin 200 or 205 (DJ equivalents of 213 and 218)... I don't think more than a 205(/218) would be required by anyone unless cam, piston, valve and porting changes have been made... in which case I would like to communicate with you on your engine mods and findings... you most likely won't require any "advice", but I would like to hear about extensive engine mods... mine will retain the stock configuration... I have a 1200cc street fighter for speed.

Have fun and if I am "not around" to answer any possible questions (I have a somewhat irregular schedule at times), I would recommend asking Retro Rich.. He has a mechanical mind and a healthy grasp on the tuning philosophy.

Radio Shack Shims:
Radio Shack Part # 64-3022
Package of 100
Steel Flat Washers
20 each: #2, #4, #6, #8, #10

They are in the Hardware section of the store -- In the plastic pull out trays that are divided into sections.. Plastic bag... Looking at the bag I would say we are using the #4 washers.. anyway it is the second from the smallest... we "miched" em several years ago and can't recall, they are like 0.019 or 0.020 or pretty close to that neighborhood.. they work! -- Oh yea, they now cost $1.99/pkg -- inflation.

Any "washer/shim" of similar thickness (0.020") with a hole big enough for the needle to comfortably slide through and small enough for the needle head to sit on will work just fine.

I could write another entire page on "tuning techniques", but it has already been done in what I consider a comprehensive and accurate manner... use it as your tuning Bible -- Factory Pro http://www.factorypro.com/tech/carbtun.html

Don -- AKA "Scars" :cheers:
 
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#28 ·
Runnin' Smoooooth Now!!!

I just performed the "Scar" method on my '06 VTX C this morning and my hat is off to ya Scar!! Last week my pipes and Kury Pro-R showed up in the mail and I was anxious to put them on over my 4th vacation only to be let down by the fact that after installing both on my bike...it ran rich.:( After precisely doing everything in the above order ( including putting the stock jets back in the carb and throwing the ones that came with the Kury back into the container they came in) that Scar recommended, my machine runs like a dream. Before performing the "scar", you could pick black boogers after riding my bike with the Kury jets installed! ( I might be exaggerating a bit!) But now it is a whole different machine!!! Words can not describe how proud I am of how it is running now. I stumbled on to this web site bummed out looking for a resolution to my problem and if you are reading this for the first time and are thinking of doing anything else beside the "scar" method...FORGET IT. Do the "scar" and you will be thanking him as I am!!
Signed... ONE PROUD VTX OWNER - THANKS SCAR!:patriot:
 
#30 ·
I dont know if anyone looks in this area anymore or not but here goes...... HELP!!! This is kinda weird. I have the biddy box mod and the kiwi mod. (pretty free flowing) I have 2 shims and the A/F is at 2 turns. My plugs are the problem. The right front plug looks like its running rich. The right rear is close to perfect. The left rear is (now get this) half perfect and half rich. The front left one looks good too. What to do?
 
#31 ·
The various plugs througout the bike will look different.. so how is the bike running? That is the main thing, tune by performance... if you have a bunch of snowwhite plugs, then you have something to think about (lean).. but if there is some soot on the plugs then don't sweat it.. if there is some tan on the plugs.. don't sweat it... tune for performance.. most of the big boys (bigger engine builders) run around a 12:1 a/f ratio and most on these boards would think that is too rich... it just depends on which "school" you are coming from and what type of performance you expect and in what part of the power band.

Here's a dyno run that many would think is too rich, but the bike runs fairly good for a street bike
 
#32 ·
Scar .. you the man !!! After two different rejets(one when the pipes were done and one when my hypercharger was put on) my bike was running ok but always felt like it was missing something. After doing some research here on the site I decided to take the plunge and put everything back to stock and apply Scars technique. My bike which has a Kury Hypercharger Pro S and Hard Chrome pipes has never felt better. Very responsive through all the gears and just feels like whatever if was missing is now there. Scar .. hats off to you brother. You the man !!!!
 
#35 ·
a/f screw

ok, I have done a few things this week to the bike. First I removed the pair system per this sites suggestions and the bike ran fine. I then made a new air cleaner (biddy box) using a cone air cleaner I found at autozone an matching breather. I am also running Samson Warlords with baffles in them. Last night I did this carb mod with 3 shims since I am considering this a "heavy breather". The only thing I did not do yet is adjust the A/F screw. The bike runs like crap as it sits right now. Driveable but ugly actin'. Anyway, this A/F screw, I have big hands and I can't seem to get to this thing. Looking for some suggestions on this. I have tried the .22 casing and the bullet connector but I cannot get my hand in there to put enough force to loosen it. Any suggestions? Am I going to have to spring for the "real" honda tool for this?

Last question, how far off is this a/f screw with the stock setting? Just curious what it may be at now. Must be way off judging by the way it runs. I have verified I have no vacum leaks or kinked hoses, etc. I think it is all in the adjustment since I cannot get my paws in there. Is 3 shims ok or should I have done only two?

Thanks for any help as I am sure these questions are something youo all have heard a 100 times!

Kurt
 
#37 ·
ok, I have done a few things this week to the bike. First I removed the pair system per this sites suggestions and the bike ran fine. I then made a new air cleaner (biddy box) using a cone air cleaner I found at autozone an matching breather. I am also running Samson Warlords with baffles in them. Last night I did this carb mod with 3 shims since I am considering this a "heavy breather". The only thing I did not do yet is adjust the A/F screw. The bike runs like crap as it sits right now. Driveable but ugly actin'. Anyway, this A/F screw, I have big hands and I can't seem to get to this thing. Looking for some suggestions on this. I have tried the .22 casing and the bullet connector but I cannot get my hand in there to put enough force to loosen it. Any suggestions? Am I going to have to spring for the "real" honda tool for this?

Last question, how far off is this a/f screw with the stock setting? Just curious what it may be at now. Must be way off judging by the way it runs. I have verified I have no vacum leaks or kinked hoses, etc. I think it is all in the adjustment since I cannot get my paws in there. Is 3 shims ok or should I have done only two?

Thanks for any help as I am sure these questions are something youo all have heard a 100 times!

Kurt
With 3 shims in there, be sure that you have trimmed the tit under the needle holder cap.. that will cause problems if the needle does not have free movement.

If you find something that will fit into the hole of the "D" screw, then it must be "dented" a little and rotated until the dent slips in where the "D" is and then unscrew the needle.. now you know why (one of the reasons) that I recommend removing the needle the first time that you go in there and putting a notch in the head so it can be adjusted with a flat bladed screwdriver. -- Car radio antennas have also been used... also those "blue" wire/crimp connectors seem to fit over the "D" screw and work for a lot of people.

To make things easier to work on, loosen the hose clamps on the rubber intake manifold so the carb can be rotated slightly and it will make it easier to work on the A/F screw -- DON'T FORGET TO PUSH THE CHOKE KNOB IN after you have finished working... it will be pulled out a little from moving the carb body around.. it will give you headaches if you forget and the bike will run like crap (check it now in fact if you haven't before).
 
#36 ·
Hi All.... I'm new to the forum, not cycles though. question for anybody, is the carb tuning useful for all stock bike? got an '03 1300S, runs like crap when cold, if i pull the choke, it won't stay on, immediatly starts creeping back in. wondered if Scar's carb procedure will help?
 
#38 ·
Using the choke on this engine is a bad idea.. loads up the plugs really fast.. you might want to clean them up and start over again.

Your bike doesn't want to run when cold.. lean.. turn the A/F screw out maybe 1/8th turn.. not too much at a time... just a little does a lot.

When you start the bike, do not use the choke, but instead use the throttle to keep revs up to idle speed or a little above... it will eliminate a lot of problems... the choke really is a bad deal.
 
#41 ·
You may have just purchased a new exhaust and/or air intake and are wondering how you should "tune" the carburetor. First off if you just "fire the bike up" with the new parts installed, THE BIKE WILL RUN. Depending on how "free flowing" the aftermarket parts are that you installed the bike will run anywhere from "pretty good" to "pretty lean and very nervous", but it will run. So now the bike has to be TUNED. The easiest, least expensive, quickest, most predictable and fool proof method of rapidly tuning it would be to ADJUST the stock parts that are already in the carb. Some people venturing into the "mods" game want to do them all at the same time... this has OFTEN been proven to cause problems for the neuvo MC "wrench". DO NOT remove the PAIR system during the same session that you are tuning the carb. :nono: , it is common while working with the PAIR removal to "miss" something in the process and have an open vacuum line or "other" air leak. Many who have done both of these mods simultaneously have ended up fiddling with their carb for days/weeks on end chasing their tails looking for what went wrong with the carb tuning while all the time it was an error in the PAIR system removal. There have been some war stories spread about how difficult it is to tune a carburetor.. bull hocky! The most difficult part of tuning a carb on a VTX 1300 is removing the fuel tank for the first time and figuring out how to dissconnect the electrical connectors under the tank.

So, what comes first eh? REMOVE THE FUEL TANK. Follow the directions in the service manual.. everyone should have a service manual.. the money you save in THIS carb tuning process alone will pay for a service manual. The money you save doing your first valve adjust using the service manual would buy a nice set of tools that can be used in OTHER money savings projects... EVERYONE needs a service manual..

Next REMOVE the air filter and backing plate. I won't "get into" hooking and unhooking the hoses attached behind the backing plate, they are pretty straight forward and will become part of your "learning process" of the easiest ways to rapidly navigate through assembly/disassembly.

NOW the carburetor is EXPOSED. Sitting on top of the carb you will see the vacuum chamber cover. Remove the cover and then remove the compression spring under the cover. Now gently grab the diaphram/piston rubber and pull it out.. the Vacuum piston (slider piston is what most old timers call it) is attached to the diaphram and the whole package will come out with it. YOU ARE ALMOST DONE AND READY TO PUT THINGS BACK TOGETHER.. see, I told you.. removing the tank was the most difficult part of the process... unscrewing the 4 vacuum chamber cover screws was no big deal, right?
Look at the slider piston and you will see a tappered "needle" sticking out the bottom of it, that is the jet needle. Look inside the slider piston and you will see the Jet needle holder. The jet needle holder is next to be removed.. you will see in the center of the holder it will accept a Phillips head screwdriver which can be used to "unscrew" the cam locks, BUT the "best" method is to use a small socket and fit over the head of the "cap" and unscrew the cap... I'm thinking it's an 8mm.. difficult to recall those things sometimes at my age, but you'll discover the correct size. Twist the cap counter clockwise just as tho you were unscrewing any "standard" nut or bolt and you will feel a "pop" after making a very small motion.. that was the cams unlocking.. the cap can now be removed, it is "unlocked".

Under the needle holder cap there is a small spring "screwed" onto a plastic "tit" protruding from the bottom of the cap... well actually the "tit" has no threads, so the spring is not "screwed" on, but consider it so... instead of "pulling" the spring off and distorting it's shape, give a "light force" pull on the spring while unscrewing it from the "tit" and set the spring aside. The "tit" does not protrude very far, but it must be "trimmed" for "heavy breather" mods, so go ahead and trim it now even if you are doing a "light breather" tune... Take some TOENAIL clippers (those are the large ones, not to be confused with fingernail clippers) and "snip" the "tit" in half.. that should be enough for heightened needle raising and still provides enough remaining "tit" for the small spring to be screwed back onto... set the needle holder cap aside.

Remove the needle from the slider piston.. place your shims into the needle "point" and make sure they slide all the way to the needle head with the washer/shim hole big enough so free movement along the needle is achieved. Hold the slider piston in your left hand and turn it at an upwards angle and insert the needle INTO the slider piston hole, passing through the CENTER hole in the slider piston (this process will not work for "left handers", you will have to purchase a Yamaha carburetor). Face the slider piston DOWN and the needle should be hanging from the bottom of the slider piston and sitting "on" the shims/washers INSIDE the piston.

Take the SMALL spring that was unscrewed from the underside of the needle holder cap and screw it back onto the shortened "tit" under the needle holder. Put the needle holder cap into the slider piston with the small needle spring tensioner sitting on top of the needle head. (If the 8mm socket is placed onto the top of the needle holder cap "nut" the tension is enough to hold the cap.. the needle cap holder can be easily inserted into the slider piston with this method utilizing a socket extender). Twist the needle holder cap clockwise (even the left handers) as tho "tightening" and you will feel the cams lock into place... that's it, the needle holder is locked. If enough of the "tit" was trimed, this should be a relatively easy "twist"... Hold the slider piston with one hand and "wiggle" the needle with the fingers on the other hand... the needle should "wiggle" (movement), this assures true alignment into the emulsion tube :) . If the needle is "stiff" and won't "wiggle", then the "tit" was not trimed enough :nono: ... go back and trim more from the tit until free needle movement is achieved. (If you are using a DJ needle, the tit must also be trimmed for the same reasons)

Replace the diaphram spring onto the needle holder cap and replace the vacuum chamber cover.. NOTE: There is an irregular "shape" in the cap that must be matched to it's mating surface when remounting, this is what the manual calls the "tab and air passages"... "Snug" the vacuum cap screws and continue reassembly.

Under the carb is the A/F screw (see manual), the stock screw head requires a "D" type tool for adjustment. If you slightly dent the end of an empty .22 shell casing, this will fit into the hole and can be used to unscrew the "D" screw. Take the "D" screw completely OUT. On the top of the "D" screw head will be a spring followed by a washer and then an "O" ring.. save these parts and reasemble in the same order when putting the A/F screw back in.

While the A/F screw is OUT, use a hacksaw blade or some simular device to cut a thin channel into the head of the top of the "D" screw.. this slot or channel should be wide enough for a flathead screwdriver blade to fit into for A/F adjustment. Once the slot has be cut into the screw/needle head and the screwdriver blade fits, replace the spring/washer and "O" ring and replace the A/F needle into the needle jet hole and screw IN. Take your screw driver and screw in the needle until it LIGHTLY seats or stops turning ;) ... don't get anal about this and over tighten or damage could be caused to the needle/jet mating surfaces :( . If you error on "seating", error on the LOOSE side, final tuning will not be affected by a minute discrepancy of "seating" at this stage of tuning. Turn the A/F screw OUT 2 1/2 turns with the screwdriver.

Reassemble the airbox and fuel tank.

Before firing the engine, look at the CHOKE KNOB and push it in all the way... any flexing of the carb while working on it will flex the choke cable and pull the choke out... it will not run properly with the choke pulled out AT ALL and final tuning cannot be achieved.

Shim heights:
"Open" style airbox and aftermarket "free flow" pipes... usually about 2or 3 shims.
Airbox flowing more air than stock design, but not in the "heavy breathing" class and/or pipes either free flow or somewhat restricted... usually about 1or 2 shims
Stock airbox (K&N filter in stock box is still "stock") and after market pipes... usually 0 or 1 shims
Stock airbox and stock pipes... tune the A/F screw for maximum performance...

A/F settings:
While determining proper main jet circuit settings the A/F screw should be set at 2 1/2 turns and NO adjustments made to it until the high speed circuit has been properly tuned -- Turning the screw IN leans the mixture... turning the screw OUT richens the mixture -- Fine tuning the A/F screw should be done in no more than 1/8 turn increments... very fine tuning will be even less... it is highly recommended to "slot" the "D" screw and tune the A/F screw with a screw driver... a 90 degree drive is useful if you have one... improvise.

SLIDER PISTON SPRING:
That's what I call the big spring directly under the vacuum cap and sitting on the needle holder cap. -- Most tuners that have springs of the type found in the VTX carb shorten the spring for faster throttle response... this is not necessary for the bike to operate, but you will shorten the response time if you shorten it... I would not recommend shortening it past 5 1/16"... that is the lenght of the shorter DJ kit supplied spring and is a proven entity... The Keihin spring is of slightly larger diameter wire so a "safe" fudge factor is built in if you cut it to 5 1/16", most do... you can cut it less than that if you are nervous, but you shouldn't have any problems with 5 1/16"... place the cut end DOWN into the slider piston and resting on the needle cap... uncut end UP against the vacuum cover.. that is the "common" practice (and no bannanas on boats either).

Most any needle design or jet design will work with the Keihin carb as long as they are set to the proper height and have the correct diameter... It has been my findings that the stock Keihin needle and jet work more "smoothly" if properly shimmed than some other designs because of the needle design and large diameter jet size... The Keihin design is just more forgiving and not as "touchy" as some other designs and need I say you are not required to remove the float bowl cover to change main jet sizes?... The Keihin 195 main jet suits most all purposes... if you require more than that you are past the "beginning" tuner stages and in that case you might think about a Keihin 200 or 205 (DJ equivalents of 213 and 218)... I don't think more than a 205(/218) would be required by anyone unless cam, piston, valve and porting changes have been made... in which case I would like to communicate with you on your engine mods and findings... you most likely won't require any "advice", but I would like to hear about extensive engine mods... mine will retain the stock configuration... I have a 1200cc street fighter for speed.

Have fun and if I am "not around" to answer any possible questions (I have a somewhat irregular schedule at times), I would recommend asking Retro Rich.. He has a mechanical mind and a healthy grasp on the tuning philosophy.

Radio Shack Shims:
Radio Shack Part # 64-3022
Package of 100
Steel Flat Washers
20 each: #2, #4, #6, #8, #10

They are in the Hardware section of the store -- In the plastic pull out trays that are divided into sections.. Plastic bag... Looking at the bag I would say we are using the #4 washers.. anyway it is the second from the smallest... we "miched" em several years ago and can't recall, they are like 0.019 or 0.020 or pretty close to that neighborhood.. they work! -- Oh yea, they now cost $1.99/pkg -- inflation.

Any "washer/shim" of similar thickness (0.020") with a hole big enough for the needle to comfortably slide through and small enough for the needle head to sit on will work just fine.

I could write another entire page on "tuning techiques", but it has already been done in what I consider a comprehensive and accurate manner... use it as your tuning Bible -- Factory Pro http://www.factorypro.com/tech/carbtun.html

Don -- AKA "Scars" :cheers:
Scar..need help on my carb 38MM cv Honda VTX 1300R...have installed vance and hines curizer pipes and bought a Kurankyn pro series hypercharger....and a Dynojet kit for the pipes...here is the problem...DJ tells me to install a Dj #185 on the groove #5 and 3.5 turns on the A/F screw, with the stock spring reinstalled..(K) people tell me change the following Pilot jet to #65, Main jet #185, shim the stock needle with a 0.8 shim included in their kit...so what do I do here to get this bike up and running....what parts do I use and at what settings? ..I do really need some help here and in detail please.
 
#42 ·
If you follow the Kury instructions you will be hating life.. ask others that have traveled that route.

Install 2 radio shack shims under the stock Keihin needle.. trim the tit under the needle cap holder.. it's all in the instructions above.. A/F screw 2 1/2 turns out.. your choice on cutting down the diaphragm spring.. if you cut it to about 5 1/16" then the throttle response will be quicker.. worst case scenerio is you use 3 radio shack shims.. depending on elevation and other minor variables..

Ask those on the main board about using the Kury kit and if anyone has had "luck" with this technique.. just follow the directions.

:cheers: :cheers: :cheers:
 
#43 ·
Take Scar's advise Robin_Hood. I installed the pro R on mine with the Kury kit and it wouldn't run at all and barely would even idle. Read about the Scar method on this website as a last resort and followed it to the T and have been runnin proud since. You can learn a lot of great things out here. The nicest thing about it, is it's full of people who have been right where you are and the info. you get is accurate. You will have to make slight adjustments that cater to your bike like the adjustment on the AF. Mine was 1/8 turn in do to running a little rich but now it's perfect. This method does nothing but work!
 
#44 ·
I have been looking for this post so i can bow down and worship at the alter of SCAR..... my first purchase was the hyper charger pro and with the longshots the bike was already running way rich and when i installed the hyper it didnt want to run at all , a horrible most deffinatly non VTX like performance..... a little bit of patience wrenc time and several grease coveredcopies of the scar method later , my bike runs fantastic and doesnt foul out the plugs every 3 weeks as before. I cannot thank you enough ....
I have a question though , the performance is alot better than when i originally gor the bike , im pulling 14.2 in quarter mile ( 250lb rider) so im
very please but would like to know if that number is comparible to what any one else is seeing with similar mods? thanks again for all the help
Dave
 
#45 ·
I have been looking for this post so i can bow down and worship at the alter of SCAR..... my first purchase was the hyper charger pro and with the longshots the bike was already running way rich and when i installed the hyper it didnt want to run at all , a horrible most deffinatly non VTX like performance..... a little bit of patience wrenc time and several grease coveredcopies of the scar method later , my bike runs fantastic and doesnt foul out the plugs every 3 weeks as before. I cannot thank you enough ....
I have a question though , the performance is alot better than when i originally gor the bike , im pulling 14.2 in quarter mile ( 250lb rider) so im
very please but would like to know if that number is comparible to what any one else is seeing with similar mods? thanks again for all the help
Dave
From the time slips that I've seen posted I would say you are "in the ballpark".. especially at 250... some of the slips I've seen were from guys that the wind would blow away :) -- I've never ran the "X" in the quarter myself.. strictly a cruiser for me.. well, except for blowing away $25K HD's that are trying to show off, but that really doesn't count.. I do have an inline 4 street fighter that is pretty fast tho :cheers:
 
#46 ·
I just bought this very nice 07 VTX1300 with a set of Cobra pipes on it and noticed that it had this flat spot in the mid range, and stumbled during certain phases of acceleration. With a bit of web searching I found the SCAR method. I took out the cobra jet kit, put the stock jet back in along with the stock needle with 2 shims under it (they measured .018 thick each) and dialed out the AF needle to 2 and 1/2 turns from its full closed position. I took all the plugs out and cleaned them up in the blaster since the bike was running so rich that they were covered with carbon deposits.
This seemed to have done the trick, no more flat spots and the bike no longer stumbles during all phases of acceleration.
One thing I did find is that getting the bowl off the bottom of the carb is much easier if you loosen the carb from the manifold so you can tilt it out a bit and be able to get to the philips head screws.
Other than that is was about a one hour turn around for this job based on scar's will documented instructions.
 
#47 ·
I just bought this very nice 07 VTX1300 with a set of Cobra pipes on it and noticed that it had this flat spot in the mid range, and stumbled during certain phases of acceleration. With a bit of web searching I found the SCAR method. I took out the cobra jet kit, put the stock jet back in along with the stock needle with 2 shims under it (they measured .018 thick each) and dialed out the AF needle to 2 and 1/2 turns from its full closed position. I took all the plugs out and cleaned them up in the blaster since the bike was running so rich that they were covered with carbon deposits.
This seemed to have done the trick, no more flat spots and the bike no longer stumbles during all phases of acceleration.
One thing I did find is that getting the bowl off the bottom of the carb is much easier if you loosen the carb from the manifold so you can tilt it out a bit and be able to get to the philips head screws.
Other than that is was about a one hour turn around for this job based on scar's will documented instructions.
:cheers: :cheers: :cheers:
 
#48 ·
Hey Scar,

I Have just installed the Cobra Speedster Shorts ( no baffs ) , and have the Kury Pro-R sitting in the garage , just wondering if you could tell me or if anyone else has the same set up and new what exactly was needed as far as shims and tuning , i understand that every bike will be different and location matters too but just to get me started , i just need a little help!
 
#49 ·
In one of the above posts(about 4 up) Scar recommended 2 shims. It was a similar situation with pipes and a Kury. That would be the start point. Good luck.
 
#57 ·
lean?

I am serching for some expert advice. I have cobra speedster shorts, pair valve removed, APC filter biddy box, and Scar method. The bike seams to run fine except I get a low tone backfire (souds like a loud potato gun) on decel from about 55 mph and above. It usually just one backfire on each decel. I have 3 shims and about 3 1/2 turns on A/F. If anything the bike seems a little rich. The air temp in North Carolina has been between 40 - 65 degrees. Warmer air seams to help alot. I didnt want to re- jet because I am hoping when it gets hot and humid soon this problem will go away. Just wondering if this sounds like I need to change the pilot jet and should I do it even though it will be hot soon? Thanks guys
 
#59 ·
I am serching for some expert advice. I have cobra speedster shorts, pair valve removed, APC filter biddy box, and Scar method. The bike seams to run fine except I get a low tone backfire (souds like a loud potato gun) on decel from about 55 mph and above. It usually just one backfire on each decel. I have 3 shims and about 3 1/2 turns on A/F. If anything the bike seems a little rich. The air temp in North Carolina has been between 40 - 65 degrees. Warmer air seams to help alot. I didnt want to re- jet because I am hoping when it gets hot and humid soon this problem will go away. Just wondering if this sounds like I need to change the pilot jet and should I do it even though it will be hot soon? Thanks guys
Yes, the system is lean. A factory pro series 393 #205 or 210 mainjet would most likely help a lot... the biddy box sucks in a lot of air.. as much as a bak system.. and the cobras will get ride of everything demanded of them.

The reason that you have less backfiring when it warms up is because cold air is denser than warm air and therefore when it is cooler you intake is supplying more air per cu. in. to the combustion chamber.. I would go ahead and "jet up" a little if it is bothering you.. check the plugs and see what you think.. -- btw 3 1/2 turns on the A/F screw is way too much.. this is an indicator that you REALLY need a larger main jet... you could also order a series 21 #58 pilot jet at the same time as ordering the main jets and save on shipping... main jets are about $3 apiece and pilot jet about $5 apiece.. you may not require the 58 pilot jet and I would not install it right away... just turn the A/F screw back to 2 1/2 turns and install the 205 main jet and 3 shims and see how you like it.
 
#58 ·
Carb Problem

Gentlemen,
First let me say thank you for all the good info on this website I enjoy reading all the posts and tricks you all have.
I already did the Scar method and when i started the bike today I reved it and still had a little black smoke coming from the exhaust. I have the stock box with k&n with cobra dragsters. I am wondering if that is normal or is the a/f scre still need some tuning? I know it is going to be better when i ride it but just freeks me out to see the hint of black smoke still. I appreciate the help.
Semper Fidelis
Boog
 
#60 ·
Gentlemen,
First let me say thank you for all the good info on this website I enjoy reading all the posts and tricks you all have.
I already did the Scar method and when i started the bike today I reved it and still had a little black smoke coming from the exhaust. I have the stock box with k&n with cobra dragsters. I am wondering if that is normal or is the a/f scre still need some tuning? I know it is going to be better when i ride it but just freeks me out to see the hint of black smoke still. I appreciate the help.
Semper Fidelis
Boog
With the stock box and K&N and cobras you should be using about 0.02" shim (one radio shack shim) and about 2 1/2 turns on the A/F screw.. that will get you pretty close... You have to run the bike for at least 15 miles on the highway to get it up to a reasonable "operating temp" and then make your judgements about how the bike is running and what fine tuning may then be needed... when you get it to pull good on the top end after running like that and the bottom end seems fine, then you are tuned.. don't worry about the black smoke at ignition time..

Semper Fi
 
#62 ·
I have a 2007 1300 Retro. I put the Vance and Hines Big Shots on my bike with Jet Kit, after putting jet kit in it wouldn't run well at all. But after reading Scar's article, I put the Original Jet Kit back in and turned the A/F 2 1/2 turns and it runs perfect. Thanks for the advise.....
 
#63 ·
Got some jetting questions? I have HK 2.5 classic straights on my 1300 with a stock air box. I bought the bike this way so I had no idea what is in it for jets. The bike is currently running good which is set at 4 on the clip, no shims under but there was one shim on top! Also has a aftermarket shorted spring.

So whats the deal? Did some just put the extra shim on top so they didn't lose it? What do you expert carb techno's think i should be running? There also could be a different needle cause of the shorted spring and can a guy tell if its not a stock needle?

Thanks again guys:)
 
#64 ·
Got some jetting questions? I have HK 2.5 classic straights on my 1300 with a stock air box. I bought the bike this way so I had no idea what is in it for jets. The bike is currently running good which is set at 4 on the clip, no shims under but there was one shim on top! Also has a aftermarket shorted spring.

So whats the deal? Did some just put the extra shim on top so they didn't lose it? What do you expert carb techno's think i should be running? There also could be a different needle cause of the shorted spring and can a guy tell if its not a stock needle?

Thanks again guys:)

The needle has "notches" and an "E" clip (that is the clip that slides into
the notch and regulates the needle height..) it is not a stock needle.. the washer on top of the needle can be removed and stored in your tool box.. chances are that the needle in a dyno jet needle and a shortened dyno jet spring.. who knows what jet is in there, but if the bike is running good, it doesn't matter.

Have fun
 
#66 ·
Boog: Sounds like you have it tuned "pretty close" right now..
tune for performance, not sound.. you will notice a change in
exhaust note, even at idle with various stages of tune.. but
performance tuning is what you really want..

"gurgle".. the gurgle is the sound being made by the PAIR valves still in place.
There is also some "crackle" sound produced by the PAIR valves.. it
was always there, but much easier to hear with the less restrictive
exhaust pipes installed. -- Yes, the PAIR valve removal it basically
the same as on the 1800 -- if you haven't removed PAIR systems before
then you may want a photo version of the actual 1300 to follow however
(make it a little easier).. go to the 1300 forum and post a new thread
"PAIR valve removal?".. Charlie or someone most likely has a link to
the 1300 removal.. request that specifically.. it is out there.. I have
seen it, but never saved it because I have removed several PAIR systems
from various brands/models of bikes and am somewhat familiar with the "concept".


Go ahead and ride the bike the way it is while you are waiting for the
block-off plates.. sounds like you have it pretty good right now.
(By the way.. no matter what you are "thinking".. turning the A/F screw OUT
does richen the mixture and not lean it out.. for some reason it is giving
you a "head fake" and making you think it is getting leaner..).. If you cut
the notch in the head of the A/F screw and use a flat bladed screwdriver to
adjust the A/F screw then there is no question as to where you are and it
is very accurate.. using the "D" tool on the stock configuration can be
much more inaccurate.. there is slippage.. tool rounding and a multitude
of things that can cause inaccurate adjustments that way..

:coffee:
 
#67 ·
Scar,
Once again thank you. I am just a little OCD and fail to realize sometimes it is a machine and I cant always dictate what it will do. It is set up pretty good as you have said twice now and that is it I will leave it. I know I am close enough not to worry about it. What would be the difference if any if I took the baffles out of the pipes, i want them louder, do i need to change anything?
On the other topic when the bike is rich it means too much fuel and not enough and vice versa for running lean. Am i correct on that one. That is what I was thinking anyway. I will leave you alone now but man I appreciate all this help and making me smarter in the world of tuning and performance. Thank you Sir.
Boog
 
#68 ·
Boog: Yes, rich is more fuel -- lean is less fuel.. we also call rich, "fat"..
if you run into any tuners that have been doing it for awhile, they will call it "fat".

Exhaust and baffles -- You are opening up a can of worms now.
If you just want more sound, then remove them.. if you want more performance it is a crap shoot from exhaust system to exhaust system.. depends on the original design. I have Rinehart pipes on my "X".. those pipes were built by a premier NASCAR exhaust builder (over 80% of NASCAR runs Rinehart produced pipes).. the way he does it is to get an "X" engine, put it on a dyno and design a pipe around the engine performance (with NASCAR engines he takes the ACTUAL engine from the car.. it costs a lot more.. but the "boys" are willing to pay for a winning car) ..

The Rinehart drag pipes are three stage (three different sizes of pipe from the header to the exhaust tip) -- The pipes pull quit well from the bottom end to the top end.. In the case of these pipes the price reflects the performance.. I bought mine for a little under $600 a few years back from an outlaw biker outlet.. I looked at the pipes recently and they are considerably more now.. but I stray from the topic. I also have an inline 4, 1200cc street fighter.. a friend of mine had one just like it and we wanted to see how much we could get out of the engine without spending any money.. First thing to do was to modify the airbox and then the stock exhaust.. I did a series
of exhaust mods over a period of about 1 1/2 years and tuned the intake each time for maximum performance (4 carbs/CV).. once I had what I thought was "max" out of the system I then got an exhaust system built by another guy that I know who builds exhaust among other things
(kinda like Rinehart)(this particular person holds a whole pile of national drag records on motorcycles.. he builds them).. the exhaust was built with an engine like mine running on his dyno.. took some time for him to get the perfect power curve (but then he had the formula for that engine and could and did reproduce them for the masses.. I got one of those).. anyway
when I put his pipe on I could notice a little more power in the mid range of the powerband than with the pipe I had modded over a 1 1/2 year time span.. there is only so much you can do with a "stock pipe" configuration... My other friend who modded his stock pipe virtually gutted it (more than I had mine).. His bike was fast, but a real pita to tune.. there was about a 3500 RPM window that it performed best and the rest were compromises.. so you had to tune it for the "area" that you planned on doing most of your "serious" riding.

Anyway.. I then put air pods on the bike (they are in a protected "air" area on that bike) and there was really no difference in performance between a highly modded stock airbox and full blown racing pods.. but there are major differences in exhaust systems.. it gets down to "flow design" and one of those parameters is controlling back pressure and exhaust velocity in various stages of the power band..

What the hell am I getting at?? I don't know about YOUR particular exhaust.. some exhausts can be helped in performance by removing baffles and some require baffles for the proper exhaust pressures.. Some companies design their exhausts with some "performance gains" and others "just for looks or sound"... I know of no one that mass produces an exhaust for
the "X" that will perform better than a Rinehart..

You can remove your baffles just for the "sound" and live with the results.. tune the bike for the difference in no baffles and see how you like it.. if you don't then you can replace the baffles -- or if sound is the objective, you can run it with or without baffles depending on which sound you prefer and the bike will still run pretty good... bottom line it is still a "cruiser" and an off the showroom floor crotch rocket will blow the doors off it anyway, so don't get too involved into the tuning for the race aspect unless you are a true gearhead.. and if you are there is no hope for you anyway.. hahahahaha

Hope that helps.. and don't worry about asking questions.. you get what you pay for and I am pretty cheap... hahahaha
 
#70 ·
Ok, we got a 2004 Honda VTX 1300S. I put Vance and Hines Stagger Shots and Kuriyakin Pro SeriesR Hypercharger on it. Ran rough so I removed the PAIR system and blanked the openings on the cylinder heads. Found you guys here and printed out Scar's carburetor mod. Did the mod except for the A/F screw (gonna plead ignorance here and ask if the A/f is the same as the "pilot screw" the manual talks about?

Got 2 shims on the needle and the stock #195 jet. Bike idles fine but still running like total crap on the road and falling flat on its face. When I twist the throttle when in gear, the bike hesitates and the motor wants to die like there aint no fuel gettin in there.

Any thoughts???????
 
#71 ·
Ok, we got a 2004 Honda VTX 1300S. I put Vance and Hines Stagger Shots and Kuriyakin Pro SeriesR Hypercharger on it. Ran rough so I removed the PAIR system and blanked the openings on the cylinder heads. Found you guys here and printed out Scar's carburetor mod. Did the mod except for the A/F screw (gonna plead ignorance here and ask if the A/f is the same as the "pilot screw" the manual talks about?

Got 2 shims on the needle and the stock #195 jet. Bike idles fine but still running like total crap on the road and falling flat on its face. When I twist the throttle when in gear, the bike hesitates and the motor wants to die like there aint no fuel gettin in there.

Any thoughts???????
A/F screw is same as pilot screw.

Sounds like you have an open/leaking vacuum hose... most common one is between the petcock and the carb there is a vacuum line.. when the pair system is unhooked there is then and "open" "T" connector.. either eliminate the connector and install a longer hose... install a straight through connector in place of the "T" connector OR put a vacumm cap over the open "T" that used to go to the pair system.

If that isn't it, there may be a loose vacuum line somewhere else in the system OR the vent hose from the fuel tank may have a kink in it.. several people have had that for some reason... the vent line is the one on the right side of the tank back towards the rear of the tank..

Odds are it is the "T" tho.

Bike should run on 2 shims with your setup.. get it running first... after that if it is lean from 60mph and up, add another shim...
 
#76 ·
idle speed adjustment

bought an '04 vtx 1300 c that has vance/hines exhaust and k/n filter in stock air box. noticed after getting home from picking it up that the seller had the choke not fully "off" when idled warm. with choke fully off, bike idle died. I tried turning "up" the idle knob under the intake box with no change in idle speed. is there a starting point for the idle setting...like listed above for the pilot screw? air altitude is 1200 feet above sea level...if that makes a difference.
 
#77 ·
your set up sounds like mine... My 05 was a bit lean at the start - they say all vtx's are a bit lean (thought mine was a bit more lean than normal, I am at 200' here in SoCal - had it in Idaho last Summer at 2200 feet, still ran great)... I did the SCAR mod 1 shim - 2.5 turn out on the A/F screw - K&N filter Stock A/B and it runs great... on a cold Morning I use the choke after it starts I push it in almost all the way and when it warms about a min. I push it all they way in... Runs great, idle is great, about 900 rpm (I installed a Baron tach)

Jim
 
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