SOHC.co.uk Forums > CB500/550

Poor cold starting & below par performance

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tom400f:
Not sure myself whether much can be made of the plug colour when the engine has been allowed to starve of fuel, will leave others to comment on that.

Amongst the work you mention you don't say whether the valves have been lapped in with grinding paste. There wouldn't seem to be anything else left that could account for the variation?

matthewmosse:
Has it been over reved post rebuild or similar? - more likely the tappets need adjustment or valves lapping in but I've seen the top rings smash their way completely out of the top of th piston and the engine still ran well like that - in that case there were 2 clues that all was not well - the bike was hard to start once warm and leaked oil - probably the oil leaks had more to do with past rebuild quality.

s7paul:
I'll have to do a proper plug chop when I get the chance; didn't have time today.

The valves were lapped in, with a nice even contact band.  Valve clearances are correct, and it hasn't been over-revved.  No oil leakage, and starts fine when warm.

It's clearly going to have to come apart, as I'm not happy with such a wide variation in compression.  If I can get 170+ on one cylinder, I'd like the other 3 to be just as good.  I think I'll just try to optimise it as it is, to get through the best of the weather, then strip it down later in the year.

matthewmosse:
If your lucky a bit of gentle use will allow something that isn't quite bedded in free off or a sticky ring to unstick. I've had engines stop leaking (and not because they ran out of oil!) and even up compression readings after a bit of regular light use - supposedly low milage usa inport engine in my 500/4 being one.

s7paul:
Now that I've got the compression tester I can check periodically to see if there are any changes.

Thanks all for the comments/advice.

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