SOHC.co.uk Forums > CB500/550

Sooty plugs

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JezzaPeach:
Hi just wondering if there’s an easier/technical way of telling if sooting is due to mixture rather than say slight oil consumption. I have to admit the deposit feels slightly oily but is not damp in appearance. I’m suspecting that when the barrels were off at some time in the past, for gaskets, they didn’t bother doing anything to the rings/bore. I only have to clean them a couple of times a year so it’s manageable.

McCabe-Thiele (Ted):
My thoughts are as follows.
If you are burning oil it would likely show as blue smoke from the exhaust and the oil level would drop.
It's possible that the valve stem seals have gone hard, this allows oil to get past the seals. On cold start up this might appear as smoke for a short period.

A more  likely explanation might lie in the type of use the bike has, does the engine get up to temperature thus allowing the pugs to self clean, it might be running a tad rich, or the spark could be better.

Just my thoughts.

deltarider:
The CB500 plugs will always foul if you are not regularly at 7000 RPM. I recommend the 'Italian tuning' for these bikes. Hit the highway and have it run at at least 6000 better even 7000 RPM for a while and... feel the difference in response and overall driveability thereafter! If you have planned tuning ignition and carbs - by all means - take your bike to the highway and do the Italian tuning first.

JezzaPeach:
Many thanks both, much appreciated.

McCabe-Thiele (Ted):
Deltarider makes a good point emphasising  the need to rev these engines, I always give my 400 plenty of revs once it's up to temperature. 👍

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