394 xp pressure test- can’t find leak

[Mpl127]

Hi fellas-
Trying to find an air leak on my 394, I’ll give you some background. Bought the saw off of craigslist probably about 8 years ago and it’s run off many board feet of lumber on my granberg. It was running fine, albeit a little difficult to start when it was warm. High rpm was a little low at 10k (I think). Compression was in the 145 range, thought I’d tear it down and try a new set of rings, which I got from madsens, first set of rings did not fit- too thick for piston groove- had to caliper them to reorder. Cylinder piston suspected to be for a 395 perhaps. 2nd set of rings fit. Compression the same with a new set of rings. Decide to Pressure test would not hold, steady drop from one pump on the mighty vac. Found pematex red around the manifold block between cylinder. Manifold and was indeed cracked replaced manifold and gasket. Pressure test again- steady drop ( I have saw blocked off between carb and manifold, cylinder and muffler, pressurized through spark plug hole with mighty vac). Took off flywheel and clutch to test crank seals, found red permatex on both seals. Cannot get either to bubble. I have doused this saw and my mighty vac with Dawn and water. Is there anywhere else I can look?!? I can’t quite figure out the piston and cylinder either, and the discrepancy with the piston rings!? Thanks!

 

[Yotaismygame]

Did you pull the fuel tank off and have a look around the case? Fill the oil tank up and look for bubbles in there also. Did you make sure the connections to the tester aren't leaking? Did you run the saw after putting in new rings? Psi will jump 10-20 or more once they seat. At least that's what I find.

 

[Mpl127]

Isolated tester and it’s fine, will check oil and fuel tank. Thank you. I did run it with the new rings and it died off of high idle. That’s when I investigated the manifold and found an egregious leak because it was cracked, but I have not run it with the new manifold, figured I’d better get the saw to hold pressure before I try to start it again.

 

[stihl86]

Deal with the rings later. Sounds like it’s time for the dunk test. Get a bucket, better yet,since it’s a husky, a garbage can, fill it with water and pump that sucker up. You’ll find your leak. I have removed wiring and ign
module just in case, when I ever did it. Now, I made up a regulated supply that I can apply a steady 5—7 psi.
It helps enormously when the leak may be so big, it won’t blow bubbles or hiss.

 

[Ozhoo]

When all else fails, pressure test it in a bucket of water.

 

[Totembear]

I hope you did, but I'll say it anyway. Did you plug the decomp ?

 

[Mpl127]

Yes with the decomp valve. I ended up finding it. My rubber block off between carb and manifold wasn’t low enough, very hard too see needed one bubble to hit it just right. Fixed that up and found another leak on the crank seal. I was shocked that I was able to find a new one at a local shop. Popped that in and I’m tight now. Thanks for your help.