Anyone good with flymos?

[newshound]

Old one with Tecumseh MV100s engine.

On last (heavy) use it started running a bit slow and lumpy.

Checked air filter, removed vast amounts of debris from fan, fins, etc, drained float chamber with the "button" but did not strip carb fully. The speed regulator seems to be moving freely.

Started fine and ran well for five minutes, then got a bit slow and lumpy again, sounded a bit like running rich.

Compression is OK but not brilliant, but don't these things run forever? Normally starts first pull as long as I remember to use the choke.

Strip and clean carb this time? New plug?

Any known problems, am I missing anything obvious?

[newshound]

Wonderful how hitting "enter" concentrates the mind.

[Clive George]

What was it then? (plug?)

[newshound]

Don't know yet, will try that tomorrow. Just embarrassed not to have eliminated something obvious in the first post.

[Hamster]

Managed to break the flywheel key a couple of years ago on a Mountfield rotary with Tecumseh engine after hitting a stone which caused the blade to stop suddenly. Engine went very lumpy and kicked back on starting as the ignition timing had been altered as the flywheel shifted a few degrees on its shaft. New flywheel key restored perfect running. They are made of soft metal and designed to break rather than bend the crankshaft!

Rod

[newshound]

Thanks, useful observation. I use this on banks where there is often the odd large lump of stone. I'll swap the plug first then whip the flywheel off if it doesn't fix it. (I'd expect a damaged key to retard the ignition, making kickback less likely, although I suppose if it sheared completely it could settle back in a more advanced position).