What should the compression be on a fresh top end on a Viper 90 2 stroke. 2005 Model.
I just did the top end with a Eton top end kit, (new cylinder and piston)

I am running some 40 to 1 pre mix for break in.

Compression is only 90 PSI, I did check it with the throttle wide open.

 

That may not be out of line, the original head they run on there is a low compression head. You will probably gain a little after break in.