Bonneville America Forums Forums Technical Forums Performance Mods leaving tomorrow, need quick help

hello all,
i know this has been talked about before but maybe someone can help me with my setup? got an 02 ba and just had the airbox removed kn filters epco pipes put on. the carbs got thruxton needles with one shim, 42 pilot 140 main. i left venice, ca on a trip up to bend oregon (sea level to 3500 ft) and everything was good till i got to higher elevation. it started to pop on decel and thought i needed to lean the fuel screw so turned it in and it got worse. went out to 3.5 and it got better. ok. left oregon up to vancouver b.c. (sea level) and turned it back to 3 out. got worse. backd it out a .5 turn and it got better. compression is a little low on one cylinder so i know the popping won't go away completely but the adjustments i've been making seem backwards to me. any help? going back to venice tomorrow and want a nice ride.

Well, it is only my opinion, but it sounds like when you get home you will need to go up to 45 pilots, popping on decel is a lean issue on the pilots the way I understand it. I just dont understand why it is showing up more at elevation. It should have started right away.
Mark

let me clarify my confusion...

if you climb to higher elevation there is less air. if the bike was running good before climbing to higher elevation i would think it's because it's getting more fuel than air which would mean to lean it out right? i called my mechanic (who is now out of town) and he said to lean it out and if that doesn't work take the shim out and if it is still doing it put in 135 mains. the popping on decel got worse when i leaned it out so i richened it up from 3 turns to 3.5 and it got better. help. ps. what do shims do because i just took them out.

The popping is because it is too lean. I am confused as to why you didnt have problems at sea level. It would run leaner at sea level than at higher elevations. Taking the shims out of the needles makes it leaner in the midrange. and if you lower the jet size, that will make it leaner at the topend. That is why I wouldnt change anything until you got home. I would then put in bigger pilots (45's ) so that you can run with it about 2.5 turns out instead of 3.5, you are getting close to the max you can turn the screws out now. The popping on decel has mostly to do with the idle circuit. ( the screws and pilot jets ) When you back out of the throttle and there is too much air and not enough fuel in the idle circuit, then it pops.
Mark

Change the pilot to the next bigger size and leave the mains alone. Then check your plugs and see how you're doing. Frankly, I'm little surprised that you aren't already running a 145 main at sea level with an air box removal job.

I cut Kimmy's air box and uni-filter, removed the mixture screws with a pink butt splice, slotted the screws and re-installed. We went on a night ride, and there's nothing quite like seeing your wife on her bike spitting fire out both tailpipes on de-cel. I brought the screws out to 3.5 turns, no help, on de-cell, around 3500 you get the "shot-gun" blast from the left pipe mainly...I rode it into work this morning, and the timing was perfect, right when I went through an underpass "KA-POW"...hilarious...will have to up the mains I guess...or something.

can popping on decel also be from running too rich? i thought it was from excess gas combusting in the hot pipes.

It sounds like there are two conditions being discussed here

1. Popping on deceleration is usually caused by running too lean in the idle to mid range. It is also due to pumping air into your exhaust either through the AI still being in place, or an exhaust leak at the headers, crossover, or slipons. Also can be caused by a vacuum leak but you would notice other symptoms with the vacuum leak.

2. Loud KaPows on startup or when decelerating with the throttle shut off are due to being too rich. There is a fine line between richening your idle screws to reduce popping (which works by the way) and being too rich which causes the mini explosions.

My experience with my 03 BA.