Engine shut down

[normlee]

I dug an old cmb 90 out to run in a mono. Bearings are smooth/feel good, good compression, head clearance checked and good. Started it up on bench, all good. Tried to shut it down closing the carb - no good. Finger over carb, still just runs had to stop it with belt on flywheel. Front gasket new, carb barrel good fit, any ideas? Thanks 

 

[Ray Sametz]

Sometimes running on the bench with NO LOAD on a large engine that can happen. Also carefully check the case for a hair line crack that's sucking air. B)

 

[DickJones]

sounds like the air leak problem, I use a 1/8 thick aluminum plates, , drilled one plate to cover the exhaust port, and one plate drilled to cover the carb plate, then I use my air tank, in the glow plug socket to, to pressurise the engine  in water, if it is leaking, it will show up very quickly.

mobydickk

dick jones

 

[Joern Markset]

That is caused by a leak in the fronthousing, between the steelbushing that sits on the crankshaft and the fronthousing.
Very normal if the engine has been run with bad bearings.

 

[normlee]

Thanks! Will check it