Topic: Smoke from valve cover breather hose. Not condensation.

[Msh5337]

Okay, so as some of you know, I recently bought a 1975 CB750 and have been trying to fix her up. I finally got her running a couple of weeks ago, and it seems like she has been doing really well.......until today. After I got back from a 20-30 minute ride, I noticed white smoke coming out of the valve cover breather hose. A lot of it! I've read many posts on here that say it's just condensation and that it will burn off after an hour or so ride. As much as I hope that's the case, I'm afraid it might not be. I "felt" the smoke in the palm of my hand, it wasn't oily but It kinda smelled like fuel. Not only that, while it was idling it seemed to be leaking fuel from the #1 cylinder header. AND when I shut the bike off it started leaking fuel from one of the carbs. Please tell me I'm not in as big of trouble as I think I am. If it helps, the PO had pods installed when I bought the bike and I haven't removed them yet. I'm not sure if he re-jetted for them or not.

[scottly]

Not only that, while it was idling it seemed to be leaking fuel from the #1 cylinder header. AND when I shut the bike off it started leaking fuel from one of the carbs. Please tell me I'm not in as big of trouble as I think I am.

Sounds like you may have a carb float level problem. The engine oil may be contaminated with gas, contributing to the blow-by symptom. Do the "clear tube" test to check the fuel levels first. Also, check the spark plugs for fouling, especially #1, since it is pumping fuel out of the exhaust. 

[Davez134]

Does the smoke "hang around" or does it dissipate quickly? How humid is it right now where you are? If that was your first longer ride, you have finally got it hot enough to start evaporating all that moisture inside. Also, double check float levels after setting mechanically with clear tube

Oops^^ he beat me to the float thing

[flybox1]

Okay, so as some of you know, I recently bought a 1975 CB750 and have been trying to fix her up. ........ I'm not sure if he re-jetted for them or not.

You bought a new bike and haven't been in the carbs to clean or inspect them? 
You've got some work to do Msh...like ALL of the 3000mi maintenance items. 

[Msh5337]

Thanks guys. The smoke didn't "hang around" too bad. And yeah, it was very humid yesterday, about 90%. But still, if it was just condensation it wouldn't have that fuel smell to it would it? Yeah, I've been meaning to start the 3000 mile maintenance. I'm just basically trying to see what kind of shape the bike is in before I start it.

[flybox1]

Thanks guys. The smoke didn't "hang around" too bad. And yeah, it was very humid yesterday, about 90%. But still, if it was just condensation it wouldn't have that fuel smell to it would it? Yeah, I've been meaning to start the 3000 mile maintenance. I'm just basically trying to see what kind of shape the bike is in before I start it.

Do the 3000mi maintenance, and then you'll KNOW what kind of shape the bike is in 

[strynboen]

and thage that oil (first thing to on a "new bike"...if you run it vith gas in oil..the crank vill seitse and you dont have any engine for your bike

[Msh5337]

Touché Flybox. Well I printed out the entire shop manual today and bought Hondaman's "My CB750 Book". Guess it's time to bust open some carbs. And change the oil of course.

[mystic_1]

Maybe no need to tear things apart too far yet, just pop the float bowls off, check/clean/adjust the floats, and make sure the jets are clear.

See where that gets you before pulling the rack and blasting it apart.

mystic_1

[Msh5337]

Okay, so I went ahead and removed the carbs. Wasn't too difficult with the pod filters on it. Everything looks pretty clean, but I think Scottly was right with the floats. The 2nd one is pretty bad. It's nowhere near the same level as the other three. I'm going to adjust it and clean everything really well tomorrow. But do y'all think this was my problem? Would that be enough to leak fuel out of the cylinder and cause the smoking from the breather tube?

[scottly]

Flip the carbs upside-down and take another pic, please.

[Msh5337]

Not the best quality. But here's a couple more. One from each side.

[scottly]

It's hard to tell from the pics, but it appears the #2 float may be set to a higher fuel level. The best way to check the level is with the "clear tube" test.

[Msh5337]

Okay, I just finished the "clear tube" test. #2 is definitely too high and I will fix it. But is that considered extreme? Would that be causing the fuel leaking?

[strynboen]

just put a lavnmower tank on..and make a bench test...i have mine karbs sitting for auers to test them..before put them on my bike