Smoking head help

jc

New Member
Hi,
still kinda newbie at this---Just got my 74 cb750 running/idling nice..or much better than it had been before. Drove it a couple miles in order to get a read on my plugs. After driving around town I parked it and let it idle for a few while picking up my garage. After a few minutes I noticed a moderate amt of white smoke rising from the head on the right side, above the #4 cylinder (or 3, and 4 not sure). The right side does have visibly more oil and gunk buildup around the spark plug port vs the left side--also looks pretty fresh or moist close to plug. I am attaching picks of right and left head for comparison as well as pics of my plugs (sorry there sort of crappy). Just wanted to ask some smarter folks what this may symbolize.

Little background: compression test was good way back when I started working on this bike. I've clean and rejetted the carbs a lot of times-- it's generally run very lean, up until now. Running 4 into one exhaust, 130 mains, 40 idles, just bench synced carbs, was running some older fuel, but recently filled tank. A while back I added a shot glass of Seafoam to full tank of gas.

Thanks very much,
(sorry pics not uploading--will try to add later)
 
Do you have a tube on the breather cover that leads back to the airbox? If not, it may be blowby air from the motor that is usually recycled through the airbox, which appears to be a whitish smoke but is actually water vapor 'boiling' off from the oil. If you don't have a hose there or have a small crankcase breather filter you may notice it


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I have the breather tube connected, but it's not connected to air box as Im running pod filters. Also, the #4 head has an obvious amt of gunk build up vs #1.

http://www.dotheton.com/forum/index.php?action=dlattach;topic=71238.0;attach=177268
 

Attachments

  • dirty head.pdf
    2.1 MB · Views: 171
Could be a leaky valve cover (unfortunately the CB750's engine needs to be pulled from the frame to do any sort of work on it). If I recall it has a big o-ring that fits in a groove around the perimeter of the cover.
 
Yah--I'm planning on doing a rebuild in the winter, but was hoping to drive it around a little with what's left of the summer. I guess I'm polling people smarter than me in order to determine different possibilities for why this might be occurring in order to determine severity...in order to determine if I should be shutting her down until the rebuild or if there is a temp. fix that would allow me to drive it modestly a bit more.
Thanks for reply.
 
Is it possible that you are running too lean? With pods, the air/fuel mixture should probably be checked (along with rejetting)...otherwise, that motor may be running way hotter than it should be...needs more fuel in the mix to "cool things down".
 
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