Another Leaking Carb -

[bobbyjoyner]

Hey Guys -

I know that I read about a dozen postings about carbs leaking fuel out of the intake side.. I tried multiple remedies, and I am still having the problem....
The bike is a 79 Standard, with fuel leaking from #4 almost anytime it is running (reserve or on) or running or off on (prime) - which tells me that the fuel petcocks are no at fault.

So far I have cleaned and lined the tank, installed paper filters, cleaned carbs, set float levels, re-set float levels, installed rebuild kits x4.... I am running out of things to do....

I know that the feul valve is closing, because I "table tested" the carbs with water - bowls removed, and the fuel stops properly.... if I hold the bowl on the carb, evrything works properly.... Once I screw the bowl back onto the carb and open the petcock to prime - it overflows.

Reason tells me that the bowl is causing the float to bind somehow... has anyone else run into this?

[Toolmaker Tim]

Floats

I think you are on the right track with the floats being held open by the bowl. However I had a set of floats that had the drop limiter tab broken off that did the same thing. I would set the float height and everything else and the blasted things wouldn't stop leaking. When I turned the carbs over without the bowl on, I could see the float valve was dropping too far and getting cocked so it wouldn't close. Still, measure the width of the floats and the inside off the bowl to see if they are touching.

[tarzan]

The floats could be bent outward a little catching on the side of the bowl or gasket.That is a fairly common problem.Also how high did you set your floats.Older carbs have a 25.7mm? newer are 23mm IIRC.Also under the fuel seat the gasket could leak on older carbs.On newer ones they have o-rings under the seat which leak when worn.Do you know you have the right carbs for the year?If so you dont have o-rings.Just a few things to consider.

[XSPastor]

Sounds Familiar...

Some have found that the floats can bind against the inside edge of the bowl gasket. Trim it to ensure that it will not rub.
I had one float dropping too low too. Just need to bend the tang. There's no spec for this so just make them all the same and not so low that they could bind. Turn the carb rack upright with the bowls off and make sure your problem float is dropping the same amount as the others.
Float valves can leak several different ways. They can leak around the gasket (or o-ring) on the float valve seat (depending on the year carb), they can leak because of a defect on the needle tip or the seat itself, or because of some sort of mechanical interference/binding issue.
Some guys will polish the seat valve with some polishing compound and a Q-tip to ensure that the seat is free of burrs. If you have the carbs with the O-ring around the float valve seat, make sure that the bore in the carb that the float valve seat slides into is absolutely clean and smooth to ensure that the O-ring makes a good seal.
Good luck. Stay at it and you'll figure it out!

[bobbyjoyner]

Carb Leak Corrected !!!!!

OK - So after a two months of playing with float levels, switching bowls/needles/float pins, etc. between #3 (which never overflowed) and #4 (which overflowed every time I ran the bike or opened petcock to prime.... I finally had a revelation!
If neither the float valve, gasket, float, nor bowl is the problem - it has to be the carb, right? During my second hour of bench testing the carb bank with a two liter water bottle, I was about to give up all hope of ever correcting the overflow condition.... When I held the bowl in place, the carb did not overflow.
As soon as I began to attach the bowl w/screws, it would overflow out the intake side... Then it hit me.... the atmosphere vents at the top of the carb might be at fault. I turned the carbs upside down, and filled #3 and #4 with Seafoam - which leaked out the air vent on #3, but which just pooled up in #4. I blew through the rubber hose, and air escaped into #3, but not #4.... the "T" fitting between #3 and #4 was clogged off to #4....
When the float bowl was attached w/screws and fuel began to fill the bowl, a seal was created, so pressure would build up and equalize / cancell out the bouyant force of the float ?, preventing it from raising completely to shut off the fuel flow and thus allowing the bowl to overflow!!!!!
I cleared the obstruction (old tank rust particles and what appeared to be some old gasket pieces) with a piece of wire, and sprayed through liberally with Seafoam, blew air retrograde through the hose, then screwed the bowl back onto the carb body..... NO MORE LEAK. NO MORE OVERFLOW.
I can't believe that I did not think of that one sooner....
On the upside, the carb rebuild kits I installed to try and fix the overflow condition sure make a big difference in performance - she runs smooth through all carb transitions to redline, idles like a dream, and gained a ton of power that I never knew she had......
If anyone else has tried everything, but still suffers from the old overflowing carb - give your air vents a look.......

[XSPastor]

Success!

Awesome!! Glad you figured it out!! Great work and thanks for sharing the solution with us!