Topic: carb leaking gas, checked the float, still leaking. At a loss for what to do.

[ntm1974]

bike: 74 cb350F

One of my carbs has leaked gas since I got my bike back together.  It runs fine but it always leaks before or after a ride (probably during as well)  It will eventually stop leaking when I turn off the petcock but none of the other carbs did it.  I figured I either had a stuck float or a poorly adjusting float.  I pulled the carbs, made sure everything was moving freely and check the height adjustment.  I also took out the spring loaded valve to make sure it moved freely and didn't have any crud in it.  Again, seemed fine.   Put the carbs back on the bike and turned on the gas but didn't turn on the bike.  ALL the carbs leaked but the original problem carb continued to leak after turning off the gas.

Am I missing something.  Is there something else I should be looking for?

 Also, should the carbs overflow if the gas is left on and the bike isn't turned on?

Thanks for any replies

[Anti-Johnny]

I had a problem similar to this. I put some seafoam in the tank and I think that cleared it up a bit. Or maybe just running the biket til everything cleared out cured it.

Also the PO had used some cheapie carb gaskets that were swollen and distorted.

and I always turn off my petcock now, sometimes the carbs will overfill while I was away from the bike. Sediment will build up in there and it overfills.

[CBGhia]

Check the brass overflow tube. It may have a hairline crack in it.  I repaired one with JB Weld, the full strength stuff, not the qwik stuff.

[mjstone]

You might want to check your overflow tube to see if its cracked.  If it is than the carb will leak even with the petcock off because its still emptying the carb bowl.

MJ

[gibber]

In answer to your question- Gas will flow to the carbs as long as your tank petcock is open. It is a simple gravity feed system.
The two most likely causes of your problem are -
1. Float levels set too high. ( you have checked this) or
2. Float needle valves are not seating.

I have a 72 350F that I rebuilt this winter and my carbs worked fine last fall when they were removed. This spring when they were re-installed I had the same issue as you are having. I did the same checks as you and even examined the float valves ,and thier seats, under a magnifying glass and they looked great. Just because I had them out I tried cleaning them with a scotch brite pad (fine grade equivilent to #00 steel wool)
I cleaned both the needle points, and the seats, and it seemed to do the trick. There must have had a thin coat of gasoline varnish on them even though they looked good. Hopefully this helps you.

[ntm1974]

Check the brass overflow tube. It may have a hairline crack in it.  I repaired one with JB Weld, the full strength stuff, not the qwik stuff.

I think this is it.  I set the float level so wrong that it should have allowed much gas into the bowl and it still leaked!!!  Took off the bowl and filled it with gas.  Low and behold it leaked.  There must be a tiny tiny crack in it somewhere because I surely can't see it!  I'm going to try to jbweld the whole thing to see what happens.  Otherwise, off to ebay.

Thanks for the replies guys.

[twinegar]

I'm glad I read this, my 75 CB550 is doing the same thing from #3 even after removing twice and replacing the float valves with neoprene tipped ones. I bet a cracked brass overflow tube is the culprit.

[Nortstudio]

I was told you can use heat shrink on the cracked tube as well. 

Good luck, leaking gas is no fun

[ntm1974]

I did the JB weld on the tube.  It worked great.  I let it set for 24hrs and put it back together.  Leak is gone. 

Thanks for the great tip. 

[phil71]

shouldn't you be able to solder a brass pipe like electrical wire? Sand the glaze off of it and flow some solder down it?

[flybox1]

I was told you can use heat shrink on the cracked tube as well. 

Good luck, leaking gas is no fun

this will work as a temp fix, but will gas might deteriorate the tubing after a while, and possibly cause more carb clogging goo to passs where you dont want it.
measure the OD of the stand pipe, and find some brass tubing at a hobby store with the same ID.  cut a section the same length of the stand pipe and fit over your cracked pipe.

[KingCustomCycles.com]

Check the brass overflow tube. It may have a hairline crack in it.  I repaired one with JB Weld, the full strength stuff, not the qwik stuff.

  soldering works excellent for this.