CB750 leaks fuel from vents

[monteboy84]

Hi gents,

My 1978 CB750K runs great, and the carburetors are beautiful, like new basically. I have one problem though, the carburetors leak fuel from the vent lines when the bike is sitting on the kickstand (jiffy stand). I think what's happening is the bike leans enough to the side that a good amount of fuel flows to the left side carburetor, and spills out the vent tube.

Would replacing the float needles take care of this problem?

Thanks all,

-matt

 

[scrubs]

first of all... determine exactly which carb(s) is overflowing. Two cheaper and more likely things to check first..
take all the bowls off and eye ball the floats for any that drastically appear out of true and height in relation to the others.
Then 'carefully' clip the bowls back on trying not to jam the floats. I had the exact same problem turns out the
floats were just getting caught on the bowl. If that still doesent fix it then next I would look at adjusting float height.

To check the float height without removing the carbs you can Connect a piece of clear tubing to the float bowl drain tube, bend the tubing up against the outside of the float bowl and turn on the float bowl drain screws. The gas will rise in the tubing and you can take your measurement by observing the top of the level of the fuel in the tubing, as it will rise to the same level that is in the inside of the float bowls. do each carb in sequence.

after that is set I would then look at the needles but my money is on stuck floats or wrong height.

 

[rockcitycafe]

ditto, the 750 carbs shouldn't overflow if a: the petcock doesn't leak b: the float needles and seats are good c: the float height is correct d:the drain screw gaskets are good

 

[monteboy84]

Thanks for the replies guys.

The float levels are all fine, I had the carbs off for cleaning and rough sync'ing, and checked all the floats at that point. That being said, I'll double-check them with the clear tubing this week.

On sticking the floats in the bowls, it's a 78 model, so the bowl screw on and go on straight very easily.

I hadn't thought of the drain screw gaskets before, but I don't think it's that either, since it really doesn't leak until it's leaning to the side.

Thanks again for the help, I'll double-check those items.

-matt

 

[Tim]

Do the floats move completely freely (should be LOOSE) and are you sure the offending carb's floats actually still float?

You should be able to determine which carb it is - remove the overflow hoses if you have to. You could also have a cracked overflow tube in one of the bowls.

 

[monteboy84]

Do the floats move completely freely (should be LOOSE) and are you sure the offending carb's floats actually still float?

You should be able to determine which carb it is - remove the overflow hoses if you have to. You could also have a cracked overflow tube in one of the bowls.

The floats move freely in all the carbs.

I'll check the tubes as well, that seems logical.


-matt