That saw should have 150psi + after a new top end rebuild. Does the cylinder have a compression release? If so, it'll reduce compression to about 90psi when depressed. If it indeed has a decomp button, make sure it's pulled out when you do the test and also make sure it pops out when you start the saw.
It can take 5-10 tanks of fuel for ring to seat. Compression goes up then - but more like 10-20 PSI. 90 PSI is low after a new topend. You SURE you have a good reading? Schrader valve in plug coupler? Or you have an AWFULLY BIG squish. Run a few more tanks thru saw - a little heavier on the oil - say 32-35:1
I build a schrader valve interface at the carb inlet. Just me "engineering" something to try to get a pressure test. I also was using a bike pump which frankly sucked. I need to get a lower pressure gauge to put inline to get a better reading.
