Have a small portable compressor, craftsman, decent for trim install and
such, easy to carry up stairs.

Was working great, now it will run and run, but never gets the tank
above 20 PSI. I find no leaks in the tubing, the check valve is free, I
took the head off, the two loose pieces of shim stock that they use as
reed valves look OK, but is there a way to test these? Without a spark
plug hole, I'm unsure of how to test rings...

Before I take it to Sears, anybody got any ideas?

Stuart