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Discussion Starter · #1 ·
I think it is a jetting issue. My mods are trinity stage 4 exhaust, K&N open lid, mild porting, extreme acceleration web cam, 11-1 je stock bore piston. I am probably around 800-1000ft elevation. I read over all the jetting articles on here but didn't find one that fit my problem. I am running 160-165 mikuni jets, stock needle clip in the middle, with 25 pilots 1 1/2 turns out. The bike pulls real hard off idle to half throttle. I took off today to race a buddy and as soon as I started moving I pinned the bike wide open and it just instantly fell on its face. If you slowly accelerate the bike past half throttle it will accelerate but very slowly and run like crap. It doesn't sound like it is hitting any rev limiter or anything it just starts cutting out real bad. I trail rode the bike all day today and it pulls hard as long as you don't get much above half throttle. It climbed everything today you just can't pin it wide open. I was going to do a plug chop but I don't know if I have enough area here to get the thing wide open the way it is running now. Just wondered if it sounds like a lean or rich condition.
 

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Your midrange is your needle, I'd richen it up a notch and try from there. If that doesn't do it, try bumping a size on your mains. You shouldn't have to increase much, your mains shouldn't be too bad where they are at 1k feet.

You haven't specified any backfiring or popping, and it's not overheating so the jetting can't be horribly off. But a bad needle adjustment can cause one heck of a midrange stutter. Also make sure the diaphrams are seated well and free of tears.
 

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Discussion Starter · #3 ·
It didn't backfire or pop at all. Never overheated either. I run the engine ice and it was covered in mud today but never had any overheating problems. It was just strange how hard it pulled thru the mid range just when you got above mid range it started acting up.
 

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IF you've gone through all the jetting issues and checked the diaphram(s), another issue could be your float(s) adjustment. If the float(s) is out of adjustment one way it will spew fuel out of the overflow hose(s) and give you the impression the bike is running slighlty rich, if its out the other way it will prematurely use all the fuel in the bowl(s) under harsh acceleration, first stuttering and ultimately stalling if you keep pushing it.

check your fuel line as well for clogs, and your carb for build up.
 

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Discussion Starter · #5 ·
went up one size on the mains and problem solved. Did a plug chop and had the nice tan ring down on the porcelan. Plug looked good. Hard to believe one size off would make that much of a difference.
 
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