1972 CB750k2 blows smoke

[jboyer9387]

My 1972 honda blows lots of smoke on hard acceleration. On normal riding it does not smoke near as much. It idles well, runs very strong, and does not foul the spark plugs. It leaks oil on the left side of the engine near the exhaust. Any ideas as to my problem such as bad valve guides or oil rings. Any input would be apprciated. Thanks

[Re-run]

Well some people have reports some smoke on HARD riding. Another cause is if you had the engine bored out. the added pressure can sometimes cause a little blow by of the rings.
It could also be worn valves or rings. I would suggest doing a compression test and see what your numbers are.

[brcree]

  Hummm sounds like valve guide seals................does it use alot of oil?

[jboyer9387]

It uses about a quart in 2-300 miles. Also, it leaks oil when not running from the oil tank to the crankcase. I replaced the check valve and spring but this did not help.

[Re-run]

Draining into the crankcase does not really hurt anything but the quart every other fill indicates constant oil use.

[bear69]

I would have thought that smoke under acceleration would indicate worn\scored bores. If the smoke was apparent on start up that would suggest valve guide seals.

[jboyer9387]

It smokes a little on start up but when warm it smokes more but not a great amount. Only on hard accelleration to near redline does it blow a thick cloud of smoke. When I run it at normal speed, it will blow a small amount of smoke.

[Re-run]

What color of smoke? I suppose we should ask that.
Black smoke is excess fuel. Blue is oil.

[jboyer9387]

It is fairly white. Maybe a little blue. It definitely smells like burn oil.