Rebuilt Husqvarna 266 won't rev

[Oldtoolsnewproblems]

So I got a Husqvarna 266xp that is dear to me. Was my first saw (found in the trash) and the first 2 stroke tool I ever actually took apart and put back together into better shape than when I started! Was the start of an addiction but I'm getting off topic.
Fast forward and I finally have a backup saw that works better than the 266, so I figure it's time to do a recipe. Saw only ever had 90psi compression but started very easy, but clearly didn't have the power a 66cc saw should. So I bought a no name piston, did a full case tear down and rebuild. Cylinder had some discoloration but no groves so I just put in the new piston and gaskets. I deleted the base gasket to try to get a little free power, and since I wasn't sure why the compression was low. Although right before closing the case I checked the old ring, and it had about 1/8 the gap, so I think that answered that. Wich is weird to me as it looked really good inside.
Anyways new piston rings end gap looked good, don't have my notes but it makes 165psi now. Deck was like .027

Well it still has a tiny vacuum leak I can't find, loses 1psi in 5 minutes, not great but not enough to stop me from taking it for a test run. Started up instantly, idles better than it ever did, nice and low.

But now when I tune the high mixture, got it 4 stroking, it only revs to 9-10k, and is very low power in the cut. With a 22" bar it drops to look 6k in the cut best I can tell.

I'm going to try to find that leak, but I'm getting conflicting info if that is really bad enough to cause my problem, or a trivial amount. Holds pressure a little better, it's vacuum that leaks a bit faster.

My fear is that the piston is wrong somehow. And that the timing is all messed up. I didn't think ditching the base gasket would change it that much. Muffler doesn't seem clogged but I don't see an obvious way to know that. I could try running it with no muffler and ear plugs, assuming that's safe for the saw.

Looking for pointers, I've tuned and built many a vw motor, but 2 strokes are a new beast to me.

 

[Ozhoo]

Welcome to AS. Holding pressure but failing vacuum leads you towards a failed crank seal. Also, pressure test your carb to 7psi to make sure that the inlet needle is seating correctly. What are your carb settings? If you're far out from 1 & 1 something is wonky. Test it with 1 & 1 out from the stop and see how it goes.

 

[RED-85-Z51]

A small leak like that shouldn't be a huge huge issue, ive had gasket deleted saws with big base leaks still start and run good but hard to tune. Kill it at the end of a cut...see how the plug looks.

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[Oldtoolsnewproblems]

Crank seals were all new and the crank sealing faces looked good. I when found replacement orings for the oil pump. Not gonna lie, I was hoping maybe 30 min of running would get the leak to seal lol. I haven't re-checked yet but I'll do that.
It's got the factory carb and set to the manual, which was pretty spot on, didn't need more that a 1/4 turn either way.
When you say pressure test the carb, you mean just put 7psi on the fuel inlet?
Also didn't know you could color check a plug on a2 stroke. Same rules apply as a4 stroke plug?

 

[RED-85-Z51]

For the most part same rules. White is kiss of death. I try to get to a medium cocoa brown color.

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[Huskybill]

Check the air leak again. What size is the cylinder, A? B? C? New am pistons cover A and B I been told.
Did you adjust the low speed jet screw? Sometimes it takes a few times to adjust it correctly.

 

[Cantdog]

Concerning your air leak......did you replace the O-rings that seal the oil pump to the case and the seal carrier on the flywheel side when replacing the seals? These get over looked a lot.....and just another place to leak.....

 

[trappermike]

Your small air leak will not affect top end power at all. I suspect a plugged mufler screen,fooled my friend on a 266,he put in new piston,carb kit etc.,but was simply a plugged muffler screen...
Or it could have carb problems not allowing fuel at high speed.

 

[Oldtoolsnewproblems]

If anyone comes across this thread in the future, here's the end of the story: clogged tank vent. Poked a needle thru it and it ran great immediately. Still need to replace the vent tho

 

[KASH]

Oldtool thanks for posting the cure nothing pmo more than an unfinished thread.
Kash

 

[Northerner]

I find it a little hard to believe it started fine before with 90psi.
Once under 100 psi I find they don’t run at all or very poorly


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