Mystery smoke!

M

mktsc

Active Member
So I've had some trouble keeping my bike running, but have noticed that when it IS running, a mystery smoke appears when the bike is warm. It's eminating from somewhere behind the brake pedal. On the right side of the bike bottom rear of the crankcase by the swingarm mount. It smells like oil smoke, but not BURNING oil smoke, more like something coming from a crankcase vent. It's not dripping anywhere, and my oil level isn't going down, however it is visably noticable. Is there a crankcase vent somewhere around there that could be disconnected or something? I seriously cannot find the source of the smoke. I checked for loose bolts on the sidecover thinking that might be it, but everything's nice and tight.

Has anyone ever seen this? Bike is a CB360.

-MK
 
This is a sign of electrical grief to come. All the brit bike guys know that the electrical system actually runs on smoke. That's right smoke flows inside the wires. When an electrical component fails the smoke leaks out and the electrics are done.
 
Maybe I can borrow some of this from some of the MG guys, lol:

Lucas%20Smoke.JPG


But seriously, I have no idea where its coming from...
 
How close is the smoke to your rectifier? Is the battery still holding it's charge?

loudest143
 
are you sure it is not coming out of the breather hose? there should be a black hose coming off the top of the engine and is routed to that area.
 
check to make sure there isn't an oil seal dripping oil onto the exhaust... that's what happened to my 400f once, a quick tighten of one of the bolts and problem solves
 
Thanks for the responses. Definately too much smoke to be electrical, plus it smells like oil. I'll check for a breather hose. I also checked tightness of all bolts in the immediate area, and all were tight.

-MK
 
i just went out and took a look at my '71 350 thinking they might be similar. my breather hose is routed from the top/back of the engine, goes over/between the carbs, infront of the battery, and terminates down below the swingarm. if you still have that area pretty stock with side covers on the bike, it would be difficult to see it unless looking for it. i still think that is what it is....from your description.
 
That's awesome, thanks! I'm going to look at it when I go home for lunch. I don't have my sidecovers or air cleaner covers on, so I should be able to see it pretty easily.

-MK
 
barring an oil leak onto exhaust, you're fine-it's a breather. My cb750 does the same thing. I had a '62 Chevy 235 that scared the hell out of me because of it's crazy down draft breather. Evidently in our day of enviro-friendliness, smoke/fumes are a sign of scariness. Ain't no thing,man...
 
Right you are! Since I had the tank off to chase various other issues, it was easy to see that vent tube, and follow it right down to where the swingarm mounts. That concequently is the source of the smoke!

Thanks again guys!

-MK
 
It took me awhile to figure it out myself, on my '77 CB750F. It wasn't subtle either... as soon as I came to a significant stop, the thing would smoke like it was on fire... Mostly because of the curing high-temp engine paint, but the breather hose definitely contributed to the plume :D
 
I had the same issue on my 75 CB360. The smoke was coming out of the breather tube that goes from the top of the motor to and exits out the bottom of the bike. Some smoke is O.K. Excessive smoke is a sign of worn rings or valve seals, etc. My rings were bad as well as the valve seals, guides and intake valves. Have somebody ride behind you and see if there is blue smoke coming out of the exhaust pipes.
 
I noticed this smoke before I did the valve tappet adjustment. They were WAAAAAY out (like 2-4 turns of the adjuster screw).

I'm sure that probably had something to do with it, LOL...
 
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