I got a Honda TRX 90 that will not run. I really didn't notice it smoking when it ran last. We tried pull starting it and it finally started after a long time and it ran like crap and wouldn't idle. I checked the compression on it with the air cleaner and lid off, the throttle wide open and couldn't get more than 80 psi. out of it. I added a teaspoon of oil in the cylinder and it shot up to 210 psi. So does this mean the piston or rings are shot? I was hoping the valves just needed adjusted, but seeing it rise after the oil it makes me think it might need a overhaul. I've rebuilt a few 2 strokes but this will be my first 4 stroke.
I spent the extra and bought a Honda cause of their last forever reputation. This bike can't have more than 40 hrs. on it. Thanks DennisC

 

That would indeed suggest rings. A leak-down tester could confirm that.

Unusual for a Honda or any other brand to have a problem like that with that low of hours. Possible intake air leak, or unfiltered air getting around the filter? Overheated? Ran low on oil?

 

I haven't checked yet for a intake leak, the air filter looked sealed up and pretty clean. The atv is only 3 yrs. old and the oil was always changed twice each year. Its never been abused, it was only ridden by my 9 yr. old around the yard. Thanks DennisC

 

yes, indeed the rings sound like they are worn or have lost tension. You'll need to hone the cylinder and put new
rings in, but it might be better if you go the extra and have the cylinder bored and a oversized piston put in.

which ever you do, be sure to put new valve seals in and check out the valve springs and stuff too.

 

Before you tear it down check your valves first. I will bet the intake is tight. Intake .002 and exhaust .003.

 

I go along with this suggestion as tight valves is usually the problem. I find it hard to believe the rings are shot after 40 hours.
I know...it doesnt explain the rise in compression after the oil was added, but its free and cant hurt to try.

 

Hondabuster has a good point. I suppose it is possible the oil you added got slung onto the valve or something...

Anyhow, I'd plan on doing a tear-down, but check the valve gap first as it would only take a second.