Leaky valves on RT125

[djsbriscoe]

I have just done a compression test on my RT125 engine and it shows good compression (170psi 12 bar) but the gauge needle rolls backward in between compression strokes. To me this points to a leak in the valves. There is also an unusual deep throaty sound to the engine that sounds to me like the problem is the exhaust valves (again). The engine will not start unless I put a small quantity of petrol into the cylinder, and then only runs a few seconds (not surprisingly).
This problem started when I found white deposits in the inlet manifold condensed onto the rubber connecting piece. I have since cleaned the carb in my ultrasonic bath (after squirting with carb cleaner) but no change. It appears that the deposits (burnt or otherwise) have clogged the valves although I have yet to confirm this. It is also possible that the white deposits originated from the cylinder after being blown back through a leaking valve.
Before I do yet another leak down test with my compressor I'd like to hear other thought on similar experiences.
I might eventually get the cylinder head completly rebuilt with new valves/valve seats etc as I appear to have got a bad head. Not long ago I had the OEM valves seated into the OEM valve seats after a similar problem with a compression leak.



David.

[djsbriscoe]

Took the cylinder head off and sent it to the cylinder head shop in croydon. The intake valves where leaking oil (valve stem seals leaking or I didnt fit them properly) and the piston crown had oil on it. I've had the valves honed and reseated properly. Now I have to reshim the head as the inlet valve gaps have closed right up (the exhaust valves still have a small gap).
The original valve buckets are the shimless type (one piece with the size printed on the underside) but the replacements from MZ are the 2 piece shim and bucket type (shim over bucket). Bought 1 off 2mm baseline shim and the bucket it fits into to measure the gaps. Here's hoping that this all works out or I'll have a useless lump on my hands.