lean?

[miclea0317]

I have cobra speedster shorts, biddy box, pair removal,and scar method carb set up. My bike seams to run fine except if I dont slowly let off the throttle when going aprox. 55 mph+ the bike has a low sounding boom from the exhaust. Sounds kinda like shooting a potato gun (only way I know to explain the sound). Does this sound like it is running lean or that that the pilot jet may need to be changed. Currently the air temp has been around 50 -65 when this occures. If it is warmer it does not seam to be as bad. I am trying to avoid changing out jets because I know before long it will be hot and humid here in NC.

[Screwjack]

miclea0317: How many turns is the A/F screw at? You should have started with 2 1/2. If you are getting the backfiring on decel, the carb is too lean, turn the A/F out an 1/8 of a turn at a time.

Here is what I did and experienced;

I just did the VTXexhaust.com mod and I installed a Kury Hi-Five intake, then I did the scar mod with 2 shims and set the A/F at 2 1/2 turns.. First good ride I had a fair amount of backfiring on decel. I pulled over and turn the A/F screw one 1/2 turn out (richen), the backfiring stopped. I then pulled over and turn the screw back in (leaning) 1/8 of a turn, got some more backfiring, although not as frequent. So I turned the screw back out that 1/8 and I think she runs great. Pulls real nice at low rpm and at the high end, no backfiring.

I think that they say if you have to go more than 3 full turns on the A/F screw, you should add another shim. How many shims did you start with? I think three is the max.

Hope this help...:choppersm

[Goldsmith]

Still have the pair valve installed? If so that sounds like it could be your problem.

[Screwjack]

miclea0317: How many turns is the A/F screw at? You should have started with 2 1/2. If you are getting the backfiring on decel, the carb is too lean, turn the A/F out an 1/8 of a turn at a time.

Here is what I did and experienced;

I just did the VTXexhaust.com mod and I installed a Kury Hi-Five intake, then I did the scar mod with 2 shims and set the A/F at 2 1/2 turns.. First good ride I had a fair amount of backfiring on decel. I pulled over and turn the A/F screw one 1/2 turn out (richen), the backfiring stopped. I then pulled over and turn the screw back in (leaning) 1/8 of a turn, got some more backfiring, although not as frequent. So I turned the screw back out that 1/8 and I think she runs great. Pulls real nice at low rpm and at the high end, no backfiring.

I think that they say if you have to go more than 3 full turns on the A/F screw, you should add another shim. How many shims did you start with? I think three is the max.

Hope this help...:choppersm

[miclea0317]

I took the same route. To be honest I need to check to see if I have three or four shims, I played around with so many configurations I dont remember. I atleast have three shims and I am at 3 1/4 turns on A/F. I dont really feel like the bike is lean except on decel just because of the pop back. It doesnt sound like it did when I was tuning and it was definately lean making the cracking pop. I was wondering if it is to rich if it could cause it to pop back like my bike does. The APC filter I used for the Biddy box really lets in some air. I even cut a piece of plastic to shield the front of the air filter on the inside.

[Screwjack]

Hmmm, you might have to check with some of the experts here on the board. I am pretty much a novice when it comes to the carb tuning stuff. I got a lot of advice from a couple of guys and just wnet with the advice and then richened up the mixture once I got the popping on decel. It all worked out and the bike seems to run great. I think 3 shims and 3 1/4 turns on the A/F sounds a bit much, but again, i am just a novice att his stuff. You may try to start att eh beginning and make sure you got all the vac lines nice and tight from doing the pair removal. Also, make sure you main needle moves freely after you cut the "tit" in the cap, if it doesn't move freely, you may not have trimmed the "tit" enough...

good luck and let us know how it turns out:choppersm

[Charlie D]

3 shims sounds a little high and 3 1/4 on the A/F is a bit over the top too

you only want to shim till you remove the flat spot on a hard roll on any more is just dumping raw fuel you won't burn.

when you start getting over 3 turns on the A/F you need to do a plug check if the plugs are black you are open to much if they are still very light you may need to go to a 58 pilot with the A/F set at around 2 turns