Topic: Why are my carbs leaking gas?

[Tretnine]

When my bike sits my carbs are leaking gas from the bottom by the drain or purge valve / overflow dealhoo. So, I put on a different rack of carbs and now they're leaking again. I assume fuel is flowing into the carbs when the bike is parked, but why? And why on two different sets of carbs?

[Markcb750]

It is due to the imperfect seal of the float needles, either due to contamination or wear.

I always turn off the fuel petcock when the bike is parked for more then a few minutes. 


Mine does this less with rebuilt carburetors, but it still will leak if I forget to turn the petcock off if it sets for a week or so,

[Tretnine]

Really? It's not coming from the seal where the bowl meets the rest of the carb, it's coming from the actual overflow nipple with the hose on it. It was also flowing for a long time, like overnight and it pretty much drained my gas tank.

[kghost]

Because gravity will cause the fuel to flow to the lowest point if there is nothing to stop it.

What stops it is the float valve.

The carb float acts against the valve and shuts off the gas into the carb when the carb has the proper amount of gas.

No shut off = overflow.

Things that cause overflow:

Improper float height.
Sticking float pivot pins.
Bad float valve or float valve seat
Trash under the float valve.

All the above can be caused by numerous factors...Number 1 being dirty carbs

Sometimes when a bike is parked....the toasty engine expands the fuel and you get a little dribble if your on the high side of the float level spec.

[Tretnine]

looks like I've got to pull the newly installed rack back off and clean and reset float heights. huzzah.

[kghost]

Dunno Heff...your 350F carbs should have an overflow tube.....

[Tretnine]

cb550k from 78. It's totally got an overflow tube attached to float bowl it's a couple of inches long (maybe) and it's a tube, you know, so when your carbs are too full it drains out there. But yes, it's attached to the same place as the drain and comes out the same hole, but it's not a problem with the drain screw.

[Redman]

If you have brass standpipes in your bowls for overflow, you should look for hairline cracks in the brass. You will need a magnifying glass as they can be hard to see. Just a thought.

[Tretnine]

If you have brass standpipes in your bowls for overflow, you should look for hairline cracks in the brass. You will need a magnifying glass as they can be hard to see. Just a thought.

It was coming out too fast to be a hairline, I think, but I really like this. This is something I never would have thought of and something I will look at the next time I have them apart.

[ekpent]

Not sure if this applies to your situation but one of my 750's after I bought it would leak fuel when left overnight. Even though the petcock was on off,the gasket etc inside the unit was bad and still sending gas to carbs. Replaced it with a know working extra and never leaked again.

[grumpy]

I'm dealing w/ the same issue right now.

start going thru the things on kghost's list

[kghost]

Dunno Heff...your 350F carbs should have an overflow tube.....

hmmm... maybe... stop making me look stupid though.   
oh well... perhaps, i did that on my own.   

I was wondering if you had super secret special carbs.......Like mini CR's or something....