200cc 163FML Intake noise/hiss

[n_dorphin]

Hey all just bought a project bike and got it started.
Its running a 163FML 200cc Chinese lifan motor.

Valve clearance set @ .06mm intake and exhaust.
When turning the motor over slowly I can hear a hiss from the intake/carby.

When started it was running very rough and backfired thru carby and stalled.

I'm assuming a worn valve, or bent valve?
Any way to check without removing the head?

Thanks All, Jas

 

[my67xr]

is it just normal compression/suction you can hear ?
eg the compression pulling air/fuel through the carby

 

[n_dorphin]

Its seems to suck air in ok, but when on the compression stroke It seems to be hissing out.
Not sure if this is a normal sound and leak or if its indicating a buggered valve?

 

[DHZ_XR8cing]

.06 valve clearances could be the problem.
Not familiar with the 200cc engine but try .006

 

[my67xr]

as Damo suggested,
are you running .06mm clearance ? that may be a bit tight when it warms up
also the valves may need relapping into their seats to help it seal?

most of the horizontal motors run .003" int, and .004" on the exhaust
so maybe try .08mm on the intake valve and .1 to .12mm on the exhaust


another common fault with the vertical motors is the intake manifolds crack,
id be taking it off and checking it out to be sure

 

[n_dorphin]

Hmm ok.
I will check the manifold tonight and try your valve settings. Will post back results. Thanks

 

[n_dorphin]

Intake valve leaky. Pulled apart this morning.