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Discussion Starter · #1 ·
I recently did the following modifications, Yoshimura full exhaust, Pro-flow air filter, holes in air box, Wiseco 11.1 piston ,port and polish head and Jetting 150 left 155 right.
The problem is gearing down or quickly releasing throttle when load on motor develops a backfire. Any suggestion.
 

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join the club ive been trying to get my popping and backfiring problems to cease. good luck
 

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throw 25 pilots in... backfiring (as you do described) is usually caused by a lean pilot circuit. Check your plug to be sure you have the right color. The Carb 101 sticky is very useful.
 

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Yes, you're too lean on your mikuni mains unless you're at a very high elevation. Even with a full airbox lid you need more fuel up top than that.

Try closer to 165/170, could need even more but it's a good starting point.
 

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Discussion Starter · #6 ·
Thanks guys for the prompt replies. I took all suggestions and went to work. First task, checked valve clearance, (too tight) adjusted intake 0.13mm exhaust 0.15mm.
Went a step up on mains 155 -160 ,adjusted needle to the third setting and also went one step in pilots (25) .Still experiencing popping at times put I’m determined to cease the problem. At this point I noticed gains in throttle response and power.
I been hearing positive feedback on dynojet needles, if I applied this step would I see positive gains?
:thumbsup:
 

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Discussion Starter · #8 ·
Pilot’s screws left 3 turns, right 2 turns(stock settings) I will increase the mains 160-165. Thanks again.
 

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160-165 mains and 25 pilot stopped my popping.
 

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lol, I chuckle every time i see your avatar, Papis.
 

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I have this same popping when I let off the gas.

1000ft asl
25 polits
150, 155 MIKUNI Jets
Clips at 4th position

Full exhaust with open air box
 

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up the mains into the 170 range, 25 pilots and change the needles to dynojet or gytr
 

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I don't know what kind of needles came with the kit. What makes you think I need to change them to dynojet or gytr? Anywhere I can buy just the needles?
 

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the stock needle just can't flow enough fuel when you start modding like you did, I played with what you have years ago and when I changed needles the bike just worked better and was easier to jet
 

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ShawnTRD said:
I don't know what kind of needles came with the kit. What makes you think I need to change them to dynojet or gytr? Anywhere I can buy just the needles?
Just remembered I got some needles, I dont have the carbs anymore so I dont need the needles, Dynojet needles.
 
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I thought backfire was running too rich no lean. I pop and backfire when i let off the throttle when i was hauling ass at high RPMs.
 

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Popping on decceleration is running to lean in the main jets, increase the size
 

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Runing to rich causes a different set of problems,it will die out and loose power,
 
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