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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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#3 ·
1300 runns like crap

i have a 2005 1300r in the shop and i can't figure it out. It idles fine, even revs up fine. when i put it in gear and throttle up it falls on its face. the bike has a hypercharger and v&h longshots. i called kury akyn and jetted to their specs.any help would be appriciated.
scott
 
#4 ·
islandcycle said:
i have a 2005 1300r in the shop and i can't figure it out. It idles fine, even revs up fine. when i put it in gear and throttle up it falls on its face. the bike has a hypercharger and v&h longshots. i called kury akyn and jetted to their specs.any help would be appriciated.
scott
Forget the Kuryakyn jets...they're all wrong.
You'd be better off with stock carb parts. Just set the A/F at 2-1/2 out, and stick a couple (2-3) shims under the needle. Very easy.
Stock slow - 55
Stock main - 195
Stock needle

If you want to get fancy - you can experiment with larger Keihin jets....but that setup will be a much better starting point.
 
#6 ·
islandcycle said:
i have a 2005 1300r in the shop and i can't figure it out. It idles fine, even revs up fine. when i put it in gear and throttle up it falls on its face. the bike has a hypercharger and v&h longshots. i called kury akyn and jetted to their specs.any help would be appriciated.
scott
Howdy
Kuryaken to prevent being sued seems to jet every thing fat. We could not get over 40 MPH and found out that we did not have the seal on the slider installed correctly. then it did all kinds of weird stuff but would ran better. So off to the Honda shop and found out that the choke was stuck in the closed position. I assume that my partner jamed the cable when he took it off or put it on. Got that fixed, leaned the jetting ( we are at 6000 ft above sea level) runs like an ape about to get raped.
 
#7 ·
I had already had the dealer put a dynojet stage 1 in the bike with my pipes. After putting on the Hypercharger I figured it was a simple a/f adjustment. Nope and the dealer swapped out the pilot to a 62, told me to pick it up and it ran great. I hit the throttle and all sorts of hesitation and it fell over on its face at wide open throttle. To avoid more charges I decided to use the garage and thousands of dollars of tools where I store it, at my buddies.

I now understand and have no fear. I actually put back in a 185 at 2 1/2 turns and clip 4 with one shim and it runs excellent. It does feel like it has a slight flat spot. I am going to a stage 3 kit but wanted to have a base to be able to go back to if I ran into trouble.
 
#9 ·
Retro Rich said:
If you have the stock main and pilot, I'd put those back in. Smoother fuel delivery, easier to tune. But, this writeup is pretty famous out there and very good. Has helped a lot of people (including me when I started tearing into mine).
Thanks, going to go read it in entirety. I am actually thinking of going to a stage 3 (220 jet) as the pipes are wide open and a buddy said his runs very well. Any thoughts on that?
 
#12 ·
Hhhhmmmm; try a Factory Pro/Keihin Style 200 (I think they have that size) with no shims and see what it does. If it's still having some flat spots, go up one size or shim the main on the next size up from what you've got with 1 shim, progressively work your way up to 3 shims. If you have to go to 3 shims and still having flat spots, go up to the next size main jet with no shims, etc., etc. Shimming on your main jet delivers more fuel, more quickly on the main circuit if you follow me (I'm sure you do).
 
#13 ·
Retro Rich said:
Hhhhmmmm; try a Factory Pro/Keihin Style 200 (I think they have that size) with no shims and see what it does. If it's still having some flat spots, go up one size or shim the main on the next size up from what you've got with 1 shim, progressively work your way up to 3 shims. If you have to go to 3 shims and still having flat spots, go up to the next size main jet with no shims, etc., etc. Shimming on your main jet delivers more fuel, more quickly on the main circuit if you follow me (I'm sure you do).
Ok, here is the question. I ordered a Dynojet stage 1 kit and the dealer put it in. When I pulled the jet it says 195. Now, is there a way to tell if they truly did anything as i hear that the vtx comes with a 195 anyway,
 
#181 ·
Now I am confused

So I bought my VTX Aug 08. First thing that had to go was the pipes. All was great except for some popping on Dcel and thought I needed to jet the Carb. I bought a DJ stage one kit. have not installed it yet b/c of what I read here that my stock is the same as what I bought, eiher that or I am mis reading. So is this going to solve the problem, or do I need to get one of Greggs A/F tools? Help
 
#14 ·
The DJ 195 and Keihin 195, although they share the same "number" are not the same size. The DJ 195 is smaller than the Keihin 195 (a Keihin 195 actually interpolates out to a DJ 208); so, the way to tell if they did anything is if you're running the DJ needle (needle with a clip). If you are, they did put in the stage 1 kit with a DJ 195 (the DJ needle and Keihin jet styles don't work well together at all, due to different design; and if I remember correctly, the DJ jets do have a "DJ" stamped on them somewhere near the numbering/size). Thus, you're running a smaller main jet than what the carb came with from the factory.

Make sense?
 
#18 ·
High Altitude Almost Stock

This is a great article. Thanks for posting. Would like to ask a more specific question though. I live at 9500 and work at 6500 feet. I purchased an air box cover with a nice "V" cutout to provide more air. Since I ride at such high altitudes, would I be able to compensate with just an A/F admustment?
 
#19 ·
RockyVTX said:
This is a great article. Thanks for posting. Would like to ask a more specific question though. I live at 9500 and work at 6500 feet. I purchased an air box cover with a nice "V" cutout to provide more air. Since I ride at such high altitudes, would I be able to compensate with just an A/F admustment?
If you have stock pipes, then you will probably only have a minor A/F adjustment to make for "perfect" tune... at those elevations, depending on how it is set now you may require nothing... look at the plugs.. tune by response.

If you do have to make an A/F adjustment.. you might want to cut the spring down while you are working on the carb.. will give you faster response time.. not necessary to make the bike run tho. :cheers:
 
#20 ·
Thanks again, Scar. I was hopin it might be that simple. Just seems to lag a little when goosed but quickly catches up.

After reading the article I was particularly interested in cutting down that spring to improve response.

What would you think of using a tach to monitor the final adjustment of the A/F while idling? I was thinking that maybe finding the spot where the rpms are highest while gently tweaking?
 
#21 ·
RockyVTX said:
Thanks again, Scar. I was hopin it might be that simple. Just seems to lag a little when goosed but quickly catches up.

After reading the article I was particularly interested in cutting down that spring to improve response.

What would you think of using a tach to monitor the final adjustment of the A/F while idling? I was thinking that maybe finding the spot where the rpms are highest while gently tweaking?
Yea, that's pretty "old school" for getting them running... but for "riding" I've found that tuning for response is more satisfying.. that's what the "big boys" do also (racers)... you don't really need to utilize the method that you mentioned and it would be a real crap shoot if it came out "right" performance wise.
 
#22 ·
Main Jet change

Hey Scar.
I've attached a hyper charger and it works great when your on the throttle.
I would like to change the main jet as it bogs out at the low end. It idles fine, it just dies out a bit when i give it a little gas. Do I have to take the carb off to change the main jet? Do you have a quick way of doing so? I will be riding in the mountains in a couple weeks and may have to change the jet again.
Thanks in advance for any help.
Ian
 
#24 ·
Hey Scar.
I've attached a hyper charger and it works great when your on the throttle.
I would like to change the main jet as it bogs out at the low end. It idles fine, it just dies out a bit when i give it a little gas. Do I have to take the carb off to change the main jet? Do you have a quick way of doing so? I will be riding in the mountains in a couple weeks and may have to change the jet again.
Thanks in advance for any help.
Ian
Ian: Whatever you do, you do NOT have to remove the carb... If you are only running the hyper and stock pipes then a simple A/F adjustment should suffice (or possibly ONE shim under the needle head, no more).. If you are running "free flowing" pipes then you will have to shim under the stock needle with the stock mainjet two or three shims depending on your pipes... that would be approx. 0.040" to 0.060" under the needle head... read the beginning of this thread carefully and you should have no problems.

If the bike is "tuned" for the elevation that you live, then riding to a higher elevation will make it run a little richer... no problem, it will still run... if you do this a LOT then you could run 89 or higher octane at your "home" elevation and switch to 87 Octane fuel when you "head for the hills"... this will lean it out a little.. don't worry about it tho.. a little on the "fat" side is ok...

Have fun on the ride.

Don
 
#23 ·
Take the four screws out of the bottom of the carb that holds the float bowl.Once this is removed you will see the head of the main jet with the slots cut into it for a flathead screwdriver.Remove the jet and replace with new.
 
#25 ·
X Flame air box w Clayton Mod

Scar, Retro,
I have a 2006 VTX 1300R and have serious carb problems now. I performed Clayton Mod putting 5 holes in each pipe- bike ran fine. Installed K&N air filter-bike ran fine. Purchased and installed Brown county X-Flame air box cover and bike ran rough...would run better with choke pulled quarter way out. Talked with Honda dealer and he recommended Cobra stage 1 rejet kit to be installed, so I had that performed and the bike was stuggish on initial throtting and run like a bat out of hell once RPM were higher. But, by the time I got my bike half way home from the honda shop which is about 10 miles away the bike didn't even want to run. It kept choking out all through mid-range and the only way to keep it running was to have the throttle quarter way open. Mechanic called Cobra and they recommended putting my stock air filter and breather back on since they didn't know how much air the K&N filter/new air cover was letting in along with the Clayton Mod...this defeats my whole intention of letting the bike breathe. I hate to think I just wasted $200. in parts and labor. Please help. Thanks Tom O'Fallon, Illinois.
 
#26 ·
Ok Tom, first off...your dealer's service department is obviously full of people that don't know what the heck they are doing. The Cobra jet kit...well, it is a waste of money and sorry to break the news to you. Your stock Main Jet (I hope they gave it back to you or you can get it back from them ASAP) is a Keihin 195; this equates out to a DJ 208. If you can get your dealer to explain why if you are taking in more air that you want to decrease the amount of fuel the carb is pumping through---then I've obviously got something to learn here. There isn't a main jet that is even close (they are DynoJet or DJ numbers on those jets) to a DJ 208 or 210 in that stage 1 jet kit.

Get the stock Keihin main back in there with the stock Keihin Needle (scrap that DJ needle IMHO or put it back in with the jet kit and try to sell the thing to the idiots at your dealership), I'd shim with the "Scar" method and use 2-3 shims. Just follow the instructions in his post. A/F should start at 2&1/2 turns. Stock Keihin pilot (which is a Keihin 55).

Your bike isn't running well since you have increased the amount of air, and decreased the amount of fuel. It runs better with the choke pulled a little because the "choke" on this bike is basically an enricher that dumps raw fuel in there into the carb. With the choke pulled a little, you're giving it the fuel it wants to get a more regular and adequate mixture of air/fuel.

Hope this helps.

RR
 
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