Did a compression test on the daughters 98 LT80 and found that the reason it did not want to start very well was because there is only 65 psi of compression. Question 1.) Took the top end off and found that the head had a very thick coat of carbon just on the exhust side of it, the intake did not have a trace. Qustion 2.) The piston rings were locked in the grooves but not from heat, they were carboned sealed if that makes any sense. Anyways, I cleaned the piston up which had a really thick hard coat of carbon on the top and got the rings off, there is not any marks on the cylinder or the piston. I cleaned the ring grooves and the rings move freely now, also I measured the cylinder and the piston and everything is in spec. Should I go ahead and bore to the first overbore or just put new rings and call it good. The piston has been replaced by the previous owner because there is a Wiseco piston in it and I am leaning more towards either the pro-x or factory Suzuki,(cast instead of forged). Let me know what you guys think so that I can get this thing going.
Ray

 

I think you should bore .05mm.
I recommend the Suzuki piston till you get to 1.5mm over.

 

What would cause such heavy, hard, carbon to build up? The exhaust port has a very thick layer also.

 

Stock motors are jetted fat. Along with lower rpm's and the pre-mix, what you have noticed is normal.

 

Thanks for the help, I was leaning towards boring just because it would be the right thing to do since I am on the stock bore. I have never been much of a Wiseco fan and prefer to stay with the factory pistons. I pulled out an 18 year old honda piston from my TRX250R and there was not a mark on it. Thanks again.