What should the compression read on a 250 Trail Boss. I have a hard time getting the TB to start, or when it does, to keep it runnig. At this time I am getting a reading of 100 PSI at WOT. Could this be part of the problem?

 

the book calls for 115psi on my 02 250tb, It is most likely the same on your 250tboss, did u check it
with the motor hot, warm, or cold, mine would check 100 warm then would check 95 when hot, so I
did a top end job & it starts great now!! (mine was starting hard too, very hard when the motor was hot)

 

Thanks for the info. Wish I could get it to run long enough to check it warm and hot, guess it's a top end rebuild next. How hard is it to replace the crank seals while I am at it? Or should I even worry about them till I see what happens with the top end rebuild?

 

my bike is not that old, it is a 02, so I did not replace the crank seals, don't know how tuff a job it is. do u know the history of your bike does it have lots of hours on it & many top end jobs, mine had about 130
hours on it & it was the 1st top end job, the main problem was the rings were worn the book calls for
.009 to .018 end gap mine had .040, the bore looked good & the piston clearance was o.k. But I went
ahead & went with a bore job & .5mm oversized wiseco piston.

 

The TB has a speedometer and when the cable broke it had aprox 1900 miles on it. So I guess its time.

 

I was having the same issue with my sons' '02 Trailblazer. It would not start easy especially when warmed up. Sometimes it would not stay running, other times it would not idle down. The compression on it was down to about 82psi. It is at the shop right now getting cleaned up.

 

I've heard some strange things in this forum regarding technical issues. I would think 100psi would make it run but not the best on power. Is it getting enough fuel? Is your gas tank vent plugged? Unscrew your gas cap and try again. I always try to look at the simple things before I spend a bunch of money and end up in the same place.

 

100psi is not that good & is most likely less than that with the motor hot, it has no place to go but down
lower, yes it is always good to check all the others things first, thats what I did with mine, but the top
end job was the fix, now I am getting 118psi with the motor hot & it starts as quick as I can turn the key!
hot,warm or cold.

 

You threw me for a minute. Anyone who can repair their top end in an hour from starting a thread should start his own business.