Help with Jetting

1 reply to this topic
  • Daz_426_02

Posted September 27, 2007 - 10:53 PM


Can some one help with my jetting.

I have a totally stock 2007 YZ450, only change is that it has a twin air filter.
I think it is running rich, I don't know what jets it has cause i have yet to open the carb up. The bike has between 50 -75 hours on it.

It does battle to start a bit hot or cold, and even when the bike is warm if i rev it in neutral, after i have rev'ed it there is a little bit of smoke that comes out the exhaust. Also it backfires quite a bit on deacel. Altitude is 2100ft temp is anything from 65f to 108F humidity is normally 75%+ (south africa)

I was thinking of adjusting the air-fuel mixture, if anyone has some pics and advise on how to do it that would be appreciated. Looking through the manual it looks quite complicated... I checked the valves yesterday and they all perfect.

Thanks guys

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  • grayracer513

Posted September 28, 2007 - 06:35 AM


To adjust the idle fuel mix:


An aftermarket extended fuel screw makes this considerably easier to do. Some popping on decel is to considered normal, and eliminating it through richening the pilot will result in a too rich idle.

U.S. '07's were typically shipped with a 45 pilot and a 165 main. I would doubt that any Yamaha made in the last several years would be running rich with factory jetting. If you find on adjusting the idle mixture that the screw is backed out beyond 2 1/2 turns, you need a larger pilot (and your fuel screw may drop out from lack of spring tension.

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