i thought i had it pinpointed but went on a bike run yesturday about 200 miles with alot of people and stared to get back firing out the tail pipe and some intake cough and just over hauled it redoing the intake for no air leaks ,the exhuast and even the coaster enrichner and i'm 3 turns out on pms, 35 pilot jet, 182.5 main jet,3clip from blunt end of needle with spacer and washer and everytime i try to turn the pms to get the highest idle i'm out 5 to 5 1/2 turns which is way to far is it a vavle issue ,back burns a little richer compared to the front which i was told thats cause the rear cylinder doesn't cool off as much as the front. some of the harley guys told me to plug the small hole off the left hand side of the carb mouth and it will richen up the curcit and stop the backfiring is this so? by the way their kuryakin jets which are similar to dyno jets.

sounds to me like you need a 37.5 pilot jet.. my carb is set up just like yours and with the 35 jet it ran like s*** ...its easy to put in..worth a try..

That hole they say to plug is the primary pilot air jet. If you put your finger over it while the bike is warmed up and idling and the idle changes for the better then it's likely you still have a manifold leak.

Plugging that jet would be the same as having the coasting enricher engaged all the time. Not only would the idle be richer but the whole pilot circuit would also be richer.

Maybe thats why HD's have so many problems . They just plug holes like that instead of fixing the real problem. Mikuni didn't put that hole there because they had an extra guy standing around with a drill in his hand with nothing better to do.

try the 37.5 and the 40 pilot jet still back fires and intake is leak free there is not a leak anywhere but still gets backfire and found out today for the hell of it backed out pms 5 1/4 turn and then i get no backfire but iknow that ain't right. back to the drawing board i guess.

what air filter are you using, what pipes? what jet kit are you using? Other than the pilot screw, have you adjusted the idle.

I ask about the idle adjuster because I see more and more people, seem to forget that there is an idle adjuster and focus on the pilot screw to set idle. They both work hand in hand. if the idle adjuster is not set correct, this does not allow air to enter thru the venturi (throat) which won't allow enough of vacuum to draw fuel. also float level is important as well, if it too low it will cause a lean condition since the vacuum won't be able to draw fuel, as well if it is too high it will be rich.

Try this, turn in the idle adjuster a couple turns, in increases idle. set the pilot screw for 2.5 turns out from a light seat, go ride for 15, 20 mins. reset idle adjuster to proper idle rpm.

As far as needle, might be not set up correct, depends on which needle you are using, if it is a Barons or a DJ with clip on 3rd groove spacer and no washer it is set to lean.

Erbman02 wrote:
what air filter are you using, what pipes? what jet kit are you using? Other than the pilot screw, have you adjusted the idle.

I ask about the idle adjuster because I see more and more people, seem to forget that there is an idle adjuster and focus on the pilot screw to set idle. They both work hand in hand. if the idle adjuster is not set correct, this does not allow air to enter thru the venturi (throat) which won't allow enough of vacuum to draw fuel. also float level is important as well, if it too low it will cause a lean condition since the vacuum won't be able to draw fuel, as well if it is too high it will be rich.

Try this, turn in the idle adjuster a couple turns, in increases idle. set the pilot screw for 2.5 turns out from a light seat, go ride for 15, 20 mins. reset idle adjuster to proper idle rpm.

As far as needle, might be not set up correct, depends on which needle you are using, if it is a Barons or a DJ with clip on 3rd groove spacer and no washer it is set to lean.






i'm using a k&n filter w/hypercharger ,stock pipes w/cobra slip ons w/baffles and there kuryankin jets the needle is after market with 5 grooves on it i have it set on 3 groove w/ washer on top of clip then spacer then one washer. i've adjusted the idle screw before the ride and down turned it when warm to 900 to 1000 rpm but no matter what

Have you checked for a vac leak on the vac nipple on the top of the manifold?

well, there are a few needles after market that have 5 grooves, so kind of hard to say where the clip position would be with an unknown one.

However I did have a memory lapse, is the AIS removed? if not, then it needs to be! The AIS is calibrated to dump air into stock pipes. so the AIS could be a cause. the other cause that I have seen over the years that can cause back fire are slip-ons. For some reason they just don't seal as well to stock header pipes, and I have seen this on many brands.

Erbman02 wrote:
well, there are a few needles after market that have 5 grooves, so kind of hard to say where the clip position would be with an unknown one.

However I did have a memory lapse, is the AIS removed? if not, then it needs to be! The AIS is calibrated to dump air into stock pipes. so the AIS could be a cause. the other cause that I have seen over the years that can cause back fire are slip-ons. For some reason they just don't seal as well to stock header pipes, and I have seen this on many brands.



sorry about not giving the needle brand it too is from kuryankin and yes the ais is removed so let me get this right the slip ons can cause backfiring even beging at the end of the exhuast i thought it had to be near the heads to induce fresh air to unburnt gases.