Hello, i have a 1985 Trailboss 250 that i can't get to run right. It is nearly impossible to start and when it does, it wont idle and will only stay running for about a minute if i give it gas. I've already rebuilt and cleaned the carb, and i have good spark and compression. Is there anyway it could be a timing issue?

 

1985? That might even be too ancient for OLD Polaris Tech to know anything about. It's impressive that it's still around. Hopefully someone has an idea and can assist you on keeping it on the trail.

 

What is the compression reading you have? Have you replace the crank seals,especially the one behind the front clutch? Timing is electronic through the cdi. OPT

 

The compression was just over 115 psi. I have not replaced anything other than some parts on the carburetor. It only starts well if gas is squirted directly into the combustion chamber.

 

115 is getting a little down there on compression,new top end is around 135-145,but something simple as the crank seals leaking could be part of the problem also. Has to have compression on the bottom end for the gas/oil mixture to shoot back up the transfer ports in order to crank and run properly. OPT

 

It also backfires sometimes, would a bad crank seal cause that?

 

Could be the lower compression,could still have carb problems if it wasn't rebuilt or jets stopped up,crank seals leaking,etc. Any of these could cause backfiring along with possible ignition problems,but just take it one step at a time with the easiest things first. Fresh fuel,eliminate the carb as the problem,replace the crank seals,especially if it's been sitting a while,then if it still doesn't run you'll have to check deeper. It's just a process of elimination. 87 model(I think?) was first year on a reverse limiter modules that caused problems,but from what few 85 and 86 models I saw I don't think they had em. OPT

 

Ok, i just got the thing to run for a bit. When it died the spark plug was wet, so it appears liquid gas is finding it's way into the combustion chamber. Any ideas why?

 

Low compression,leaking crank seals or both not allowing the fuel/oil mixture to atomize properly! This is the most common cause of wet plugs if the carb is ok. OPT

 

Ok, so the crank seals are behind the drive clutch on one side, and the recoil starter on the other?