Low compression after engine warms up CT 90

Bertlin08

Bertlin08

New Member
I have done a top end rebuild on my K1 CT 90, new piston, new rings, new valves (Lapped), and a new previously used cylinder bored to the oversize piston. I have everything together and the motor starts up great with tons of compression, but after riding it for a bit and then trying to start it again their feels like there is very little compression and the bike is almost impossible to start untill it cools down.

I made sure the valve gap was to spec and it was, I even tried giving it a bit more of a gap but it didnt seem to help anything. If anyone has any advice or thoughts I would greatly appreciate it.

Also i dont know if it would have anything to do with it, but when the rpms on the bike are on the lower side and its under some strain the engine seems to miss a bit studdering untill the rpms go up. Once again any suggestions would be extremely appreciated. Thanks
 
What is your piston to cylinder wall clearance? What are you running for a main jet size? Go up a few numbers because you might be running hot and lean.

Rick
 
Are you certain the clutch isn't slipping when hot ? .

To get the best AutoClutch action Honda dealer training said to only adjust it with the engine running at idle .
 
Thanks for the quick replys! I dont remeber the exact cylinder wall to piston clearance but I do remember that it was comfortably within tolerance. I do think Nate may have the right idea. I recently adjusted the clutch engagement point while the bike wasnt running ( I didnt know I should). I cant do anything to the bike at the moment, but as soon as I can I will readjust the clutch and report back. Thanks both of you for the suggestions.
 
Just go through and recheck things. Make sure your in the right stroke for valve adjustment, torque the head, check camchain tension, adjust clutch, test condenser/points

Also make sure it's running with an air filter. If it runs leaner and gets hotter then that may expose your issue faster
 
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