Topic: '76 CB750K Runs descent but smokes out #4 exhaust, troubleshooting

[stickman]

Hey folks,  I have been off the forum for several months and have always received great advice and help here. 

Just picked up a 76 750K running but smoking from the #4 exhaust.  It is a light blue oil smoke I think.  No unusual noise that would suggest broken or damages parts.  PO says was parked for approx. 2 yrs. before he tinkered and got it running recently.  Bike has not been put in service since getting it started.  Now I need to troubleshoot to determine what my issue is.  My skill level is modest.  So I have a few questions and am asking for any general info or suggestions from the group.

1.  Any wisdom in just putting the bike in service for a while in hopes that its a stuck ring and frees up?

2.  If I do a compression check, what should I look for?

3.  Other ideas?

Thanks in advance for any input...........Stickman

[ekpent]

You will be OK to run it in for awhile and see if it is a ring that may loosen up and improve. Little seafoam in that hole for a soak won't hurt and maybe a little shot in the gas tank. I have ran a little in the oil tank also for a bit before an oil change.

[trueblue]

Does the smoke clear when you rev it or get worse, bring the revs up to about 3 to 4k and hold for about 5-10 seconds,  if it clears then it is likely the valve guide seals, to test the valve seals give it a few sharp raps on the throttle, only to about 4k ish, if it gets significantly worse it is probably in your top end.

[stickman]

Thanks guys for the thoughts.  Nothing much to report yet, just wanted to acknowledge the feedback.  I poured about and ounce of seafoam on top of the pistion on #4, let it sit overnite and yesterday fired her up.  Hitting on all 4 cylinders and temp check on the header pipes showed only minor lower temp on #4.  The light blue smoke is still there but seems slightly less volume.  The amount of smoke increases when the throttle is pushed upward but nothing significant from idle.  I suspect that it may be burning off some excess oil/gas stored up inside the #4 exhaust( it has drag pipes so each cylinder is easy to keep tabs on.  My plan now is to put fresh fluids in and take her out for a run and see if it improves any.

I will report back.  Thanks again for the input.  Stickman

[trueblue]

One other thing I should add, if it gets significantly worse when it is under load it is likely your rings not sealling properly, which could mean they are worn or just stuck.