Problem
 

Ok so first race of the season last sunday.. On the start line butterflies ready to rip.. Anyway first lap half way round a mate stalls at the top of a nasty hill climb..i was sat up his arse and ended up stalling half way up after half hour of trying to kick it off nothing so had to push a mile back to van over terrain that was boggy an barely ridable (not impressed) any way fuel tank off check for spark good spark fuels getting through..but when kicking the engine over it sounds a bit flat? Not as much compression there?? Anyone any ideas what to check next? Guna have the carb off and clean that out regardless but I don't think that is were the problem lies..? Its a counterbalanced engine in a2000 ec 250 any help would be extremely appreciated?
Cheers luke

Carbwas clean as a whistle

compression gone a bit... broken reeds or piston rings?
check for scoring inside the cilinder through the exhaust hole.

Reeds are fine and rings are in tact/no scoring to end is only 12 hours old however I did find fuel in the flywheel case so I'm guessing the crank seal has gone on that side.. Would this cause it to just stop working?

Very well could cause a compression leak and low compression could and does cause hard or no starting. When you get the piston and rings out when you tear down, check the end gap on the rings. I don't know what the spec for a GG is but on most bikes anything more than .015 indicates out of spec rings. When you check the end gap, put the rings at the bottom third of the cylinder. Let us know what you find....

Before you go ripping the motor apart check one more thing.

Make sure that your slide is closing properly on your carb. If it was open a bit it will cause it not to start.

For example, this has caught me twice. After taking the bike apart and putting it back together, I routed the throttle cable wrong which caused some tension on it. I had to jump start it and it started wide open. Once I put the cable around the bars correctly it started as it should.


Good luck

I find it odd that it just konked out and that was that.

I'd personally be throwing a new spark plug in it. Pulling the bowl of the carb blowing them out, checking for shit/moisture in the bottom of the bowl., making sure the slide is where its meant to be etc. And then trying again. Did you try a bump start?

Give the engine a once over and make sure that no bolts have come undone. The crank case drain would cause a significant drop in compression.

Sounds like you might have identified it as being LHS main seal.

You said top end is fresh so I'd imagine rings would still be in spec. No harm in double checking but doubt this is the problem.

Try a bit of start ya bastard in the intake and see if you can get it to fire.

Cheers guys just waiting on a flywheel puller now am I right in thinking its left hand m27?

No didn't try a bump start.. Also once ive pulled the fly wheel and removed the stator can.i get at the seal that way and replace it?

Currently have the clutch off power valve actuator and crank gears and rhs seal looks in good nick and no play in mains at all up and down but should there be a slight rotary play with the gears meshing?