Where else to look for air leaks besides top end + left case seal??

[hellbertos]

I have been struggling w/ what I assume is an airleak for a while now and was hoping someone (or a few of you) could help me out.

The bike is an '01 YZ125. When I start it up it, the thing just starts reving; maybe like at half throtle. So, I figured, "no big deal, its got an airleak somewhere". I talked to a friend at the bike shop who asked one of the mechs there who said check the reed cage seat + boot, and base gasket. I tore the whole thing down (figured I'd do the top end since I was going to check the base gasket) and found NOTHING... atleast not obvious. Base surfaces were in perfect shape, reed cage surfaces and boot were good. Everything re-torqued to spec. Then I read in Eric Gorr's book about the left side crankcase seal which can deteriorate over time. So, I replaced that, but the bike still exhibits the overly high idle. Also, turning the idle screw on the card has absolutely ZERO effect.

Does anyone here have any advice on where else I can look and/or how to test for it (other than getting it to the shop for a leak down test)? Is there something I am overlooking?? Could this be a problem w/ my carb?? Anyone else gone through anything similar? Trying not to feel desparate... thanx in advance for any info you guys can pass along.

 

[sick 96 250]

Is it just when the bike starts up. My bike does it also and so has majority of my past bikes. Sounds normal to me, also can be a lean condition with the jetting. But if its only at start up i dont think it is that bad. there were a lot of other posts about the topic so look around and you should find your answer

 

[hellbertos]

Hmmm... well, its not just when I start it. It revs high anytime it should be idling. I mean, it does it when I start it, but if I let it warm up a bit then ride it down the block, it still over revs. The condition never corrects itself.

I did do a search on the subject and turned up a few tidbits of info, but nothing that I haven't already tried. I was hoping one of you guys out there would have some experience w/ a similar prob or know of other areas to check for leak probs. Maybe the seal on the other side of the crankshaft??

I'm at a complete loss and hoping the minds of DRN can help me out.

 

[dat dude]

Possibly a cable adjustment...

 

[reelrazor]

Hmmm... well, its not just when I start it. It revs high anytime it should be idling. I mean, it does it when I start it, but if I let it warm up a bit then ride it down the block, it still over revs. The condition never corrects itself.

I did do a search on the subject and turned up a few tidbits of info, but nothing that I haven't already tried. I was hoping one of you guys out there would have some experience w/ a similar prob or know of other areas to check for leak probs. Maybe the seal on the other side of the crankshaft??

I'm at a complete loss and hoping the minds of DRN can help me out.

The seal on the 'other side' is wet. That is, it runs the transmission oil and a bad seal there means it will pull in trans oil, making the bike smoke(blue), and foul plugs.

Unless your trans oil is extremely LOW.

I would be checking a) fuel flow. b) cable adjustment-to make sure the cable isn't holding the slide high in the carb.

You said earlier " turning the idle screw on the card has absolutely ZERO effect".

Do you mean the pilot mix screw(bottom of carb body downstream, or angled up at upstream end of carb)? Or the idle stop screw (on side pointing straight out-pushes against a ramp on the slide)?

If you truly do mean the latter, idle stop screw, then you almsot certainly have a cable issue or the slide won't sit all teh way down in the carb for some other reason.

 

[hellbertos]

Thanx RR and everyone else for the info so far. RR, I meant to say the pilot mix screw. Been reading up in the service manual. I am going to pull the carb tomorrow and see if I can sort out the problem on that end.

One question: How does one go about checking fuel flow?? Does that refer to checking jetting specs against the manual or is there actually a way to measure?.

Hopefully I wont have to jump back on here and ask you guys more stuff after digging into the carb tomorrow. Thanx again and, everyone else, feel free to weigh in...

 

[reelrazor]

Fuel flow as in supply of fuel TO the carb. It should run out of the line from the tank in a steady stream, for as long as you let it.

Usually engines will gain revs if they run out of fuel. This is because the mixture goes lean before it runs out.

Also, could be float level low/obstructed float needle valve allowing the carb to run low, giving you a 'false' lean = revs.