Fluid Dynamics et all

If a speedster is normally parked in a position where the fluid level in the front mounted full gas tank is higher than the carb inlet, what kind of problems might that cause at the carb?
Is there any device normally designed into a Weber that would prevent fuel flow under such condition?
Can gas flow freely through an electric fuel pump by gravity when the pump is not operating (I know it depends on the internal pump design, but does anyone know what the pump design is?).
How fast would fuel pump pressure dissapate after the pump is turned off?

Thanks for any insight.

Normally the fuel pump will fill the carb until the bowl is full and then the float raises up and closes an inlet valve shutting off the supply. So if your question is will gravity cause and overflow of the carbs - it should not.

Parking like you describe should not cause any problems if everything is working normally. Now if the car is vertical...that is another story.

The electric pumps I have seen all allow flow through when they are off.

I haven't checked how fast it should dissipate, but in a vented system it shouldn't take long. More than a second - but much less than a minute (my guess).

What are you experiencing?

Mike

Thanks Mike. See former thread on "Leaky Webers".

yes, if there is any leaking at the carbs, the only thing to blame can be a defective or wrongfully set needle/bowl assembly, unless is coming from the body of the carb

I don't know if a leaking inlet valve would spill gas outside of the carb. I think the gas would/should follow its normal route from teh bowl into the jets and into the barrels.

If you have leaking on the outide of the carb, something like the inlet hose or inlet screen cover or gasket or a fitting is leaking.

For an exploded view of the carb you can go to www.redlineweber.com in their tech section.

Mike

Gravity will cause the carbs to bleed fuel. If the car is parked on an uphill incline with a full tank of fuel it can easily get 5-6 PSI and seep past the needle valves.

I have seen engines with stock carbs fill completely to the top and need a tear down from it (fuel kills all the seals and it leaks like a sieve)

I sometimes use an electromechanical fuel cut off solenoid on my personal cars. Its an aircraft part but if you want one I can give you the information for it. It works good as an anti theft device, since it will not allow fuel to flow until its energized.

I don

The only exception to what Bruce says is if your fuel tank vent isn't, and it's a hot day...

Specific gravity of fuel, etc. are really beside the main point here which is- when the man parks his car with the front wheels up, the carbs leak. I'm not an engineer, or a carb tuning ace, but I troubleshoot for a living, and when there is a cause/effect relationship, the solution is to address the cause. Park the car level, and the problem goes away. I'd park the car level, and not worry about it...

Jake - I'm just curious, where is the leak path in your scenario? If it leaks past the inlet valve and in to the bowl - won't it flow through the jets into the barrel? How would it get outside the carb body?

Just curious - I will be able to sleep tonight without an answer.

Actually, I have some spare IDF 44s, maybe an experiment is called for.

I guess if there is a potential for a leak of fuel it is prudent to find a fix if indeed something is not correct...wouldn't be fun to have an engine fire..

If the front wheels are only 12" higher than the rears, there is something there.

Maybe a solenoid hooked up to a Clapper. Clap on Clap off ...

Where are you located David?

All I can say is that I have seen it happen more than 5 times in my days with the VW. Once it happened to me, but I caught it before it destroyed the engine.. It was on a sandrail that I parked n the side of a dune in Glamis to take a pic...

when the fuel bypasses the needle valve it will fill the carb float bowl and it will begin to dump down the throat of the carb. After it dumps [past the butterflies it will continue down the runners and into the intakes. You ALWAYS have atleast one intake valve open so that one will dump directly into the cylinder. The other 3 will take a tad longer but if they are even cracked open it will bleed past them also.

After the cylinders become saturated the fuel will sneak past the rings and start filling the crankcase. This may take a solid day to happen, but if you have a full tank of fuel you can fill the entire crankcase easily.

About 8 years ago I had an older customer of mine( i had been working on engine for him since I was 15) spend about 20K restoring his 66 beetle 100% to the "T". He is a local guy. I built the engine 100% bare bones stock and detailed it to the max. Even the sheetmetal screws were OEM. He drove the car for about a year and one day he called me and said "Jake, I cannot get my engine to spin over and its leaking oil out of the tail pipe, and its showing that its out of gas"

So, I drove down to take a look at it and saw it parked on a huge incline with the nose up. I walk around to the engine and looked at the "oil" and smelled it. It was fuel, not oil! The engine was so filled that the fuel ran past an open exhaust valve and filled the muffler and then started dripping out! Its a good thing that the engine was 'Hydro locked" from all the fuel, else that sucker would have exploded with any spark within the engine!

I towed the car home, got all the fuel out of the engine and noticed that the fuel had eaten the sealant away and the pushrod tube seals were ruined... So I had to do a warranty repair on the engine just because he parked it on a hill and did not understand that it was not my fault- that VWs had this problem sometimes when parked on a hill.

Lesson learned-

Don't depend on the math- just know it can happen and when it does the engine may need a teardown to remedy it.

Re: gas tank vents

I was thinking about this today on my way to a service call. A lot of us have check-valves in the vent hoses which keep the tank from going into a vacuum as fuel is used out of the tank, but do not allow fuel (or vapor) to escape out the vent. I've noticed that every time I fuel up, my tank (even nearly empty) has quite a bit of pressure built up. With the car parked on an incline, possibly the fuel in the float bowl is on enough of an angle that the needle valve is open ever so slightly, and the pressure (along with gravity) are enough to leak fuel into the bowls and down the venturis. Just a thought... I don't thinks there is a problem here, but I could be wrong.

Know I see why early Porsche have shutoffs at the tank.

I wonder if there is a simple valve we can install with a remote cut off?

Stan, you will get a pressure buildup if the vent is in backwards - test it for correct installation by the blow-through method; several replica owners have found their vents were installed backwards...

Early Porsches had a fuel petcock with normal, off, and reserve settings; Zenith carbs in particular were prone to leaking past worn float needles, and many owners would turn the gas petcock to the off position when they parked the car.

George,
With the check valve installed the other way, gas sloshes out the vent tube on every corner. The check-valve was installed to stop this.

Hmmn.

with or without a vent the gravity situation can become an issue. In the summer it would be worsened as the heat will try to make the vapor expand in the tank and help get the fuel down stream.

Yep.