Testing Compression

Discussion in '2-Stroke Engines' started by Shadeslay, Apr 19, 2009.

  1. Shadeslay

    Shadeslay Member

    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?

  2. mountain80

    mountain80 Member

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

    Shadeslay Member

    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.
  4. mountain80

    mountain80 Member

    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.