Testing Compression

[Shadeslay]

How should compression be tested "with a jack shaft", or with a normal setup.

Also I'm curious what would be the normal compression for a fairly new 50cc and 80cc?

 

[mountain80]

I had about 95 psi on my ''80'' stock at 4000ft and now have 160 with my modified head and gasket.

 

[Shadeslay]

wow 160 is awesome.

Finally figured out the right way, was a little confused at first thinking after every kick start attempt "was getting some erratic readings 60-90". But found out it's after 4-5 kick starts.


My reading at sea level with 150 miles on a 50cc is 115 psi, not sure if that's good or bad though.

 

[mountain80]

Doesn't sound bad just make sure the throtle is wide open when you do a compression check and you have grounded out the sparkplug to the engine so you don't wreck the ignition. BTW 160psi is with about 200 miles on a fresh top end rebuild and 0.050 off the head.
cheers