Carb problem! Dumping gas into engine after it's shut off.

[drdoak]

I'm hoping one of you carburetor experts can help me with a problem. My daughters 70 bug is leaking gas into the engine AFTER it is shut off. You can see it dripping onto the throttle plate. I rebuilt the carb and changed the bypass cutoff valve to no avail. This is a fairly new solex carb (less than a year old). I pulled the top off the carb and filled the bowl with gas and it slowly leaks into the engine! I can't see where or how but was hoping someone may have heard or seen this problem before and can help me diagnose it. Hate for her to have to buy another new carb. It's a Solex H30/31.

Thanks in advance,
Dennis

[Q-Dog]

I'm dealing with this problem too, but have not figured it out. Pull the top off and the bowl is dry, and the gas is sitting in the manifold. Car starts fine and runs great after the excess fuel burns off. I have another carb on my bench that I will rebuild, eventually, but for now I'm just living with the issue.

Since it seems to take at least over night for it to happen, I installed a cutoff valve under my gas tank and just shut off the fuel when I park it for long periods.
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Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[FryDub]

Is the brass dump tube for the accelerater pump circuit still there?.....Its super common for the H30/31 to lose it down the intake. Check that out.
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"4 out of 5 voices in my head say Go For It"

[otis_bartleh]

I'm having a similar problem with a 30-PICT-1, but like Q-Dog, am just living with it until I find the fix as it's still running good. It's driving me crazy though, I've pulled the carb apart a few times now trying to find the problem...
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-Adam
'59 Mango Bus
'11 Golf TDI 6-speed
'69 Bug

[ashman40]

The carb inlet (needle seat) valve should be stopping the flow of fuel into the fuel bowl before it reaches the top. When adjusted properly, the fuel will stop flowing into the fuel bowl when the level reaches about 3/4" from the top of the bowl.

OP, it sounds like your inlet valve is stuck open, or misadjusted. Excess pressure left in the fuel lines are flowing past the valve and over flowing the fuel bowl. The fuel will leak out the venturi or the vent tube once it overflows the bowl.

Remove the inlet valve and clean it out with carb cleaner. Some of the new (non-Solex) inlet valves are crap. If you flip the carb top over so the nipple/button of the inlet valve is IN... then try to blow air into the carb fuel inlet. A working needle seat valve will block the flow with just the weight of the needle sitting in the seat. If yours still leaks, replace it.

If you can, find an original Solex inlet valve and install the proper gasket below the valve. The wrong gasket and the valve with be at the wrong level. I thought the carb overhaul gasket instructions should tell you which gasket to use... but it doesn't mention the H30/31.

I did a quick search and cannot find a spec for which spacer to use below the inlet on an H30/31??? I supposed you could start BIG with a 1.5mm spacer/gasket and run the engine for a bit to stabilize the fuel level. Shutdown and remove the top of the carb and measure the fuel level in the bowl. Remove spacers until the level rises to the desired level.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[Q-Dog]

Mine is not the needle valve. The carb never overflows, and the fuel level is correct. Like the OP said, when the car is parked, the bowl will eventually empty into the manifold.
_________________
Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[mtdorajohn]

I had this problem and it was the float.

the float didn't shut the gas off because it was mis-adjusted and floated way too high before it shut the valve off. I bent the float a little and tested it. It is all good now.

second, make sure your float really floats. I had one one time that didn't float anymore and thus never shut the valve.

[drdoak]

Thanks for the info guys. It's definitely NOT a needle/seat issue. I removed the top of the carb and filled the fuel bowl with gas and watched it leak about half the fuel into the manifold, no fuel line, float, needle, seat or pressure involved. I'm trying to figure out how/where it could leak into the throat...? This engine also runs good once it's started, it's hard to start due to the engine getting flooded when it's parked. Had to change the oil due to all the gas in the oil. I'll probably change the carb soon if I can't find a fix for this.

Dennis

[ashman40]

[Q-Dog]

[drdoak]

AshMan40,

That's pretty much what I suspected (a crack in the housing) but wanted to get some other ideas before I had my daughter buy another new carburetor. I've inspected the carb several times looking for a crack but there's nothing obvious. Also, no leak at access bolt, and the brass dump tube is still in place (FryDub).

[mtdorajohn]

I agree with ashman.... a crack in the bowl that you can't see....

maybe under the screw in jet threads through to the intake.... how about removing the carb and put some gas in the bowl with food die in the gas. That way you will see where it is leaking out from.

I am not sure it JB weld is gas proof..... but it works wonders on other small cracks in metals...

[ashman40]

[donmurray]

Had a similar problem with a new Spanish made Weber. In an hour or two all fuel would leak out of the bowl, pool on top of the butterfly, then down the carb throat. The leak was not fast enough to keep it from starting or running OK. There was a casting flaw, or a fuel passage was drilled wrong. Carb body was replaced. The food coloring sounds like a good idea.

[don.ville]

Interesting theories.
Any thoughts as to what would make this happen after many years of a reliable running carb?

Swapped float needle from a good running carb, and it still floods after warm run. I pinch off the fuel line and it's still gurgling and filling the throat with gas.
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67 Standard 11 window How I Keep My Bus Alive
04 Jetta TDI Page (SOLD)
01 Mexican Beetle Hello Kitty Rescue (SOLD)
29 Ford Model A Rat Rod (SOLD)
2015 Audi A8L TDI Quattro

[PaytonD21]

I know this post is 4 years old, but has anyone found a solution to this. I replaced the idle shut off valve because mine was faulty, but I still seem to be getting gas in the intake. I have the same symptoms. Hard starts, rough idle until the gas is burnt, and smokey exhaust for the first couple minutes.

[57BLITZ]

[ashman40]

The original post above was about a carb that would empty its fuel bowl into the intake while not running. Is that what your carb is doing? There's a big difference between a carb draining its fuel bowl over time and one that is overflowing while the fuel pump is running.

The float/inlet valve control the flow of fuel into the carb while the fuel pump is running. Check for bad/dirty inlet valve; bad float; incorrect spacers between the valve and the top of the carb.

One thing not mentioned above when looking for a leak would be to remove the carb from the car and set it on a rag on your workbench. Make sure it is upright and level. Fill the bowl with fuel (full should be 3/4" from the top edge). Look for fuel dripping out. See if you can identify WHERE it is coming from. The fuel bowl should not leak.
_________________
AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[Q-Dog]

In my case, I did a rebuild (soaked it and replaced gaskets) and lowered the fuel level to a couple MMs below recommended and it seemed to help. Never did find a crack or figure out why it would drain when parked.

I eventually replaced that 30/31 pict and the problem went away.
_________________
Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[PaytonD21]

If the float is faulty and doesn't shut the valve wouldn't the bowl over fill and leak? Even with the car off?