HELP! I'm stumped...

[trooney]

How about a pic of the "gouge"?

Here you go..

 

[trooney]

For lack of a better term

 

[Sloughfoot]

It's not an AM cylinder, it's a KS. First time I've ever had this problem to this extent. I'm hoping it's the ring or cylinder. The only thing is the gouge above the exhaust port roof. Maybe that's making it so low on compression that it won't fire. I don't subscribe to the theory that 100 psi is enough to fire off a chainsaw. But that's just me

Yeh, still a problem if it did fire.

 

[Stump Shot]

Here you go..

The top 5/8" or so of the cylinder is the critical part of making compression. If there's any disruption there, it could be what's giving you trouble.
Hard to see just what's going on in the pic, but something looks suspect at the least. Whether it's glare or reflection from the camera, I can't tell. If you run your finger along and feel anything that's not smooth as glass, that's a problem.

 

[dangerousatom]

That image is a bit hard to read but I must agree^ the first 10degrees from TDC look like there's a lip-cut-line thing goin on, or the nickel plating is missing up top....? ( not that I can believe you wouldn't see a defect like that )

Random question: Is the pin in the piston for the ring alignment?

Its going to be something stupid im sure

 

[cuinrearview]

Everything I build might eventually be for sale, so I don't mess with stuff that looks like that. At 110 psi other factors start mattering more. Is the A/F ratio optimal? Sure, it has spark, but is it a good hot one? I'd bin that cylinder even if you end up finding another problem and can get it to run. It's always going to be a turd without some machine work, and maybe even that can't bring it back. Just my .02

 

[bigbadbob]

Did you ever check the squish???

 

[cus_deluxe]

that little guy? i wouldnt worry about that little guy. seriously that will not cause a noticeable change in compression, certainly not enough to make it not run. looks to me like we are just seeing a reflection on the cylinder wall that people are thinking is rough stuff toward the top yes?

 

[cus_deluxe]

and if you cant eyeball the difference between .25 mm and .5 mm then you should check ring end gap just to eliminate that as a possibility.

 

[cuinrearview]

that little guy? i wouldnt worry about that little guy. seriously that will not cause a noticeable change in compression, certainly not enough to make it not run. looks to me like we are just seeing a reflection on the cylinder wall that people are thinking is rough stuff toward the top yes?

Not unheard...

 

[drf256]

Does the saw run for a few seconds if you put some mix through the carb bore?

Did you reverse the intake block gaskets? The impulse hole is always off, even on the OEM block and gaskets. I generally chamfer all 4 holes by hand with a rounded tree burr.

 

[Fun2Cut]

Does it have a decompression valve? Is it sealing properly? I didn’t see that come up in the discussion…

 

[Nutball]

I got a heavily scored poulan going with some 90 weight gear oil on the piston and a shot of nitro fuel. I also had a 120psi ms290 not fire, though it looked good inside. I can't remember if I tried gear oil and nitro with it though.