SOHC.co.uk Forums > CB350/400
Smoking
Octavian:
Ok, so since posting I have changed the oil, stripped and cleaned out all the carbs and flushed the tank out and put clean fuel in and started her up. Cough splutter, cough splutter, still loads of smoke. I'm starting to think its blue smoke now. >:(
Octavian:
So, can anyone offer any further advice to assist me isolating the problem ?
I have run a compression test and all plugs show a slight improvement when I drop some oil in, suggesting piston rings could be the issue. So whats my best bet, strip her down and do the rings or is there anything else I should check out before committing myself to that?
Spitfire:
OK what is the history of the bike, was it running well before it was laid up ?
Is the air filter clean, is the exhaust standard, have you checked the points/timing/advance & retard unit, what colour and condition are the plugs, are the HT leads in good condition (and plug caps). Carbs all clean and float levels correct ?
Just a few ideas.
Cheers
Den
K2-K6:
If you suspect the rings it could give the characteristics you describe and would improve with oil to help it seal when you test it.
What psi reading did you get and what did it improve to?
If that is so, I would try to see if they are just stuck from sitting for a long time by doing this:- make sure that the head gasket surface is level (think it's barrel is upright on 400-4) and remove the plugs. Turn the crank to get the pistons all roughly level and spray a decent amount of WD40 or PlusGas into each cylinder enough to fill the ring gaps around each piston with liquid and leave it overnight then spin it over with the plugs in as this tries to force the compression rings into making a better seal, repeat for another dose and then try to run it.
If you still don't get good readings then you maybe forced to strip the top-end to have a better look.
470four:
My Four piston I removed just after getting the bike some 21 years ago?
I remember reading if they are continually redlined the rings break & make a bid for freedom... needless to say it smoked a tad. :)
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