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Old 04-11-2007, 10:07 PM
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Question Yz125 wont pull after half throttle after new FMF Rev pipe...

     

Hi, last week I installed a new FMF rev pipe on my 99 yz125 replacing a beat up Pro Circuit pipe and it no longer pulls after half throttle. The idle, off-idle, and midrange is great as it was before, but I definatly lost top end. The silencer is a Pro Circuit that matched my old pipe.

Things I have checked: The plug looks good...maybe slightly lean, brownish colored tip, no detonation, whiteish-brown porcalin, and a slight bit of oil around the outside. The fuel is good. It is being run in our other 2-stroke. It is 32:1 Klotz and 110 race gas. I installed a new air filter. There are no exhaust leaks. There were no other changes made to the bike with the pipe. I went from a 360 to a 380 jet and did not pick up anything on top. I have also tried three different positions on the needle and it did not help. The carb was also completely cleaned out.

The bike had a recent rebuild and ran great before the pipe. It has a Weisco pro-lite, some porting, vortex ignition, and decked head.

I'd appreciate any help! Thanks,
Matt
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Old 04-11-2007, 10:39 PM
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Default Re: Yz125 wont pull after half throttle after new FMF Rev pipe...

Check FMF's web site for jetting specs. If I remember correctly I actually had to lean the main on my 250 with the SST pipe. FMF Racing
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Old 04-11-2007, 11:41 PM
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Default Re: Yz125 wont pull after half throttle after new FMF Rev pipe...

Thanks, I tried their site and all they have is jetting info for quads and tt bikes
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Old 04-11-2007, 11:53 PM
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Default Re: Yz125 wont pull after half throttle after new FMF Rev pipe...

They used to have all kinds of two stroke jetting on their site. I haven't been there in 6 months though. When you lose one end of the rev range like that, it is wise to go rich first when experimenting, especially if it just dies like the fuel was shut off. Most modifications that enhance overwind favor leaner jetting. As was aparently YZ's case. The silencer could be confusing the pipe a little bit too, but I doubt it alone would do as you describe.

Experiment down if you are inclined to trust your ability to judge a lean condition. If not a phone call may be worth your time (to FMF).
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