I just got an 85 Polaris trail boss, in quite good condition. So, the situation i'm having is that the quad wont idle without full choke. i ride it around the yard without choke, runs fine, but instantly dies if you let off the throttle. cleaned the carburetor - did nothing, checked for air leaks, seems to be none, i just don't know what to do. i am quite fed up right now so any advice would be helpful. -85trailboss

 

if its never been apart my money would be on crank seals

 

What is the compression reading,plus how did you check for air leaks?

 

The compression is 154 with 4 pulls, i might have high compression pistons, in which my knock at idle will happen because im using shitty 87 octane gas. i need to get over to the gas station to get some premium.

 

154 psi on a 250.. That's higher than what a new one was straight out of the crate...

 

Update, nothing has changed whatsoever. it vibrates at low rpm/idle and wont stay idling without choke. ive noticed that once it warms up, it wont idle with choke on at all, and when i flip the choke to off, the rpms go up about 1000, then drop back down to stall. how would i know that my crank seals went?

 

Leak down test can show if crank seals, or a head or base gasket,intake manifold or even a case could be leaking. Main seal that would leak on these is the one behind the drive clutch.