wide open misfire Help!

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Sep 18, 2002
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#1
I NEED HELP!!!!!!!! I have a 2000 kdx 220(pipe,rb carb,240 big bore,boyssen reeds,drilled air box,b7es,running race gas and premium 50/50 at 32:1 with hp2,carb currently 45 pilot,155 main,needle in top position) The problem I have is when I roll the throttle slow it gets close to wide open without missing. If I roll it hard it won't even get close. The further down I move the clip the worse it gets. I have tried 40,42,45 pilot and I have tried 142>155 main. I have fresh gas and the cylinder piston & rings are new. I am not sure which needle I have but it was sent with rb carb.I would like to get to point of doing a plug chop but cant get it to stop misfiring.
 

Jim Crenca

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#2
Sounds like you've acquired a nice brass collection that should represent many reasonable jetting options. I assume that this misfire will not clean out when throttle is snapped open quickly and, that it sputters & pops. What needle?
 
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#3
It does not clear up it sounds almost like its not getteing enough gas but I am begining to think I need to go leaner. Is there a direct corolation between needle highth and jet size? example if the needle is in the top position and it gets worse as you raise the needle(I think this makes it ritcher) does this mean i need to go leaner on the main?
 

tedkxkdx

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#5
At wide open throttle the Needle has nothing to do with your mis fire. You are totally on the main jet so while riding at WOT does the bike feel weak and popping, then it is lean. What altitude are you at? It sounds to me like you may be running to lean of a main jet. Did this occur with the stock 160 main? As you describe your roll on and twist quick to full I further think it is main jet induced. Running the needle in the top position is not correct either. You should be changing needles if that is where your needle has to be. And since it seems you are not getting fuel your needle clip should be lower not higher. Lower clips mean more fuel into the carb and vice versa. Clip position effects 1/4 to 1/2 throttle and the needle taper is all the way to 3/4 throttle position. So placing the clip in either of the outer positions is for testing only, not constant riding.
When you ride at half throttle constant are there problems? When riding from half and quickly going to full throttle is there hesitation? If yes to either then your needle is too lean.
Hope this helps. Isolate by circuit not the overall jetting since you talked about what pilot jet you have.
 
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#6
Thanks everybody for the info. I finally found out what the problem was. I am happy that i found the problem but I feel kind of stupid. I checked the reeds the plug the gas and oil made sure my carb and filter were super clean. Then finally after changing all my jets around and posting a need help question, I took my baffle off and rode it. What a difference changing the packing in a pluged up baffle makes!! Again thanks for the help guys. Paul Talley