Hey Guys - been having a heck of a time with a 2004 sportsman 90 (2 stroke). I was reading 30psi on my old compression gauge so i replaced piston, rings, gaskets, bought a new gauge and its also reading 30psi.. Is there anything other than what ive replaced that would cause such low compression? perhaps crank seals or a something on the bottom end? any help would be much appreciated!

 

did you bore out or at least hone the cylinder when you redid the top end? crank seals would be below the combustion so should not be a fact of low compression i would think.

 

If you didn't have your cylinder bored to the next size piston, don't expect much to change. Seals can be a factor but not with that much loss of comp.

 

Did you follow the break-in procedure to seat the rings. This will be moot if you didn't at least run a honing stone inside the cylinder. The cross hatched walls give the rings "their own surface" to seat to instead of trying to seat to the smooth surface created by the last set of rings. i imagine just a stone hone could be done once, maybe twice before you'd have to bore it or replace it. There can only be 3 places a 2 stroke could lose compression. The cylinder walls (rings), the cylinder head (gasket) and the spark plug/hole (broken, cracked, cross threaded).