2166/372xt Idle Issues After Build??

[barton174]

So, I've got this 2166. 2015 saw. I took .020 off the base, still using a gasket (and yamabond), de-restrictor'd the transfer covers, beveled the lower transfer openings, .030 off the piston skirt intake side, new rings, and removed the strato splitters in the filter mount, carb, and intake "manifold"... The "spike special" treatment, basically. (also ground out the plastic center piece between the adjuster screws, so the carb adjusts with just a regular screwdriver)

I'm tuning it, and I got the top end at 12,800 for breaking in the new rings, it revs fine and all that. It also idles fine for like 10 seconds or so, then the rpm floats around a bit for a second or 2 (as it gets lean), then it dies. It'll stay running if you rev, idle less than 7-8 seconds, rev, idle less than 7-8 seconds, and so on.

I've had the carb off twice, and blown air through the jets/ports, as well as this last time, carb cleaner through everything, and it flows through the whole idle cicuit just fine.

I haven't vac or pressure tested it yet, but if it was a vacuum leak, it either would idle or wouldn't idle or whatever, right? It wouldn't idle fine and then lean out ~10 seconds later and then die, right??

Thanks,
Mike

 

[ANewSawyer]

There a lot of things that could cause that. I would open the L needle ccw a little and see if that doesn't help. But until you ressure and vac test it, you may be just masking a leak. I have one that I did a rebuild on but it has a leak, that I can't find, so I am resealing the case. You just don't know.

Now, if it died when returning to idle from WOT, I had a saw that was too rich in the L needle and killed the saw off wot.

 

[barton174]

I can go out enough on the L needle that it gets pretty fat at idle, and it'll still lean out and die after several seconds.

Thanks
Mike

 

[ANewSawyer]

Hmmm, so you hear it lean out? Like a running out of fuel sound. Does it stumble? I am at a loss. Does it come back if you blip the throttle?

 

[barton174]

Yeah, it's like you're running out of fuel. Idles rock smooth for 7-8 seconds, then raising and waivering rpm idle for a second or 2, then shuts off. If I rev it during those last 2 seconds or so, it'll bog right off idle like it's lean, then take off and rev.

Mike

 

[barton174]

Day shift bump

 

[grizz55chev]

Do the vac pressure test, stop guessing. If you can't find the leak, tear it down to the crankcase and cylinder with the intake tract and muffler blocked and dunk it in water to find leaks, ( 7 to 10 #'s psi )works every time.

 

[Marshy]

Double check the tank vent and fuel lines?

 

[barton174]

Double check the tank vent and fuel lines?

The tank ends up having some pressure in it, and it does run at WOT just fine without running out of fuel, so I don't think it has a vacuum or a capacity issue.

Do the vac pressure test, stop guessing. If you can't find the leak, tear it down to the crankcase and cylinder with the intake tract and muffler blocked and dunk it in water to find leaks, ( 7 to 10 #'s psi )works every time.

Yeah, that's what I'll probably end up doing, but wanted to post on here and see if anybody had seen the same issue before. It smells like carb issue to me, because like I say, it idles fine for 8-10s before it leans out and dies. I'm wondering if it's an issue with vacuum pulse not being enough to pump fuel in while idling or something. Maybe needs a carb kit. Maybe there is something stuck in a fuel passage from when I ground out the teflon divider for the carb limiters, even though I've blown it out from both ends with compressed air and carb cleaner. I will vac test it before I buy a carb kit, though.

Mike

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