Took 2 stroke lawwnmower out of shed, added fuel. Mower started OK, but after 4 minutes tone changed and "smoke" belched out of side. I switched off, had a look and couldnt restart,. Convinced myself the head gasket was blown so changed it. Spark ok and new plug fitted. Still wont start.

Frank DiCarlo, July 2009

The symptoms sound like the compression release valve has failed. It's the fitting screwed into the cylinder head that has a pipe attached.

Temporarily replace it with a spark plug (just happens to be the right size!). Attempt to start - please note that it will take considerably more effort to start than usual. If successful, replace the valve.

phil_saunders(a)bigfoot.com

Phil Saunders, July 2009

Being two stroke, compression & fuel mixture is the key for running, having already changed the head gasket, check the difference in compression from spark plug installed & unistalled. The only other 2 possible problems is the crankshaft seal or the rings have worn.

Macca, July 2009