I have low compression (around 60 -70 psi) on my 94' 250 Trail Boss. I'm planning to have the cylinder bored out, just wondering what size piston I should put in it. What size is the stock piston?

Any tips before I start?
Can I pull the cylinder off without removing the entire engine?

 

unless u are sure that it has never been bore out before, u are going to have to take
it apart an see what size piston is in it. then if the cylinder looks decent u can go .5mm
bigger than what was in it (the sizes go up in .5mm incurments) then take the new
piston, rings & cylinder to a good cycle shop & have them them bore & hone it to fit
the new piston & rings. the stock size should be 72mm if it is the same as the
250 trailblazer & I think it is. But check first and see what is in it & the condition of the cylinder. U should have no trouble taking the cylinder off with the motor in the quad.

 

No need to go any larger bore than you have to. Measure the cylinder. It may be possible that a quick hone job is all you need. You won't see alot of power difference just because you bore it.

 

Dont bore the jug more than you have too. Just go up to the next size and use a good piston. Boring the cylinder will not do much for power if you think it will help. While you have the motor apart get the head shaved.020 for more compression.