Topic: carburation commiseration

[donny]

I have had some gas leakage, off and on,  out the overflows. I cleaned up the float valves, etc. Quit leaking again. But now, when I turn on the petcock, I see quite a bit of gas bubbling  thru the clear inline filter, so I know it is leaking into the cylinders. But why isn't it going out the overflow? They are clear. Float height rechecked.  1976 750f. 
thanks,  Don 

[super pasty white guy]

Maybe you're just seeing the effect of evaporation out of the bowls?  How long does it sit between uses?

[donny]

   overnite.
Don

[TwoTired]

One of the properties of most materials is that they shrink with colder temps.
Fuel volume shrinkage would lower the floats, opening the float valve.
Since the supply line is shut off. Fuel in the supply line is replaced with air from the top of the float bowl chamber as the fuel in the lines fill the float bowl, till the float valve shuts again.

You now have extra air in the fuel line feed.

When you again turn on the petcock, the bubbles try to rise to the top of the containment vessel as the lines refill from the tank.

Cheers,

[donny]

 :)thanks for the info. However, I still can't see why the fuel goes into the cylinders now, and not out the overflow? ? 

[TwoTired]

How do you know it is leaking into the cylinders?

I don't think it is.

[333]

To see where the gas might be going, check the airfilter for the smell of gas.  Do the same with the oil, smell the dipstick

[donny]

the gas is going somewhere, and not out the overflow. 
yup, the oil is thin, smells somewhat of gas  & the oil level appears to be higher. The fuel level in bowls on 2 & 3 were low? I had rechecked the float levels.
When I turn on the petcock, it appears quite a bit of fuel runs thru the filter.  It didn't do that before.
Don

[mattcb350f]

I'm not sure what carbs are on a 76' 750 but I've seen carburators on dare I say snowmobiles (Mikuni's) that would leak into cylinders without leaking out the overflows. The reason they do it is because the overflows are really more just vents than anything and when the fuel gets too high in the carburator it flows out the jets and into the engine before it reaches the outlets for the overflows. In other words, the overflows are acually located higher than the lowest outlet, the jets. At any rate, I would suspect faulty needle and seat or sticky floats.