This problem is just "driving" me crazy!
After the bug has been driving for a while, the gas will start to bubble in the gas filter, almost like it's boiling, but the filter is NOT hot to the touch. I think it's either air getting into the fuel system, or a vapor lock.
I sometimes can run for a couple of hours, or minutes, then this will happen. Have to sit for a while, and hope I don't drain the battery!
Is there an easy way to do a pressure check of the fuel system?
Please help!
Thank you.
Why do you have to sit and hope you don't drain the battery?? Are you actually saying that the engine is difficult to start after you shut it off??
True vapor lock is extremely rare on a VW. Vapor lock means the fuel in the suction line going TO the pump gets so hot that it turns to the vapor phase and the pump can't pump it.
What IS common is that fuel pressure builds up in the pump and lines going TO the carb when the engine has shut off, especially when the engine bay is hot. If the pressure gets high enough, it can force the float needle valve open.
Fuel can also boil in the carb bowl and flood the engine while sitting.
It's a difficult problem to diagnose. To measure pressure, you'd have to insert a TEE in the line for a gauge.
If it DOES sound like flooding, start by making sure the float needle valve is screwed in tight and is seating.
Speedy Jim
Thanks for the reply Jim:
You ask "Why do you have to sit and hope you don't drain the battery"
Opps, I forgot to mention the engine dies, and I can't turn it over.
As this problem occurs, the engine will die (no gas to the carb), and no gas will get into the carb until the engine cools. or if I remove the fuel line from the filter, hear a slight "puff" then wait for a while (sometimes 1/2 hour) until I can turn it over again.
Right before the engine dies, if I "goose" the accelerator, I will see the bubbles in the fuel filter, almost like it's boiling..
A couple times I drained the battery with this problem.
Aha! Try this test and report back: Go on a typical drive, but this time leave the fuel filler cap loose.
If that cures it, the fuel tank is not venting.
Jim
Hey Jim:
Been there, done that (even bought the t-shirt)
2 weeks ago, I tried that, and the same problem.Thanks.
Steve
OK. Test the flow from the tank. Take the hose off the pump inlet and let it flow into a gas can (or something). If you have to, jack up the front of the car. Do this test OUTSIDE and with the engine cold.
Let it flow a while. You should get a steady stream. If only a dribble, there is a blockage. Some Supers had an in-line filter under the tank (there is NO screen in the tank), but I don't think '74 did.
It could even be a blockage inside the tank; a lump of crud floating over the outlet.
Pretty rare, but a suction line with a pinhole can starve the pump by sucking in air.
Jim
Steve, I had the exact same problem with my 74SB for two years every summer. After many tries at different solutions, I put an electric fuel pump under the fuel tank and no more problem. I got the pump from auto zone for about 30 bucks. They have it listed for the VW in their computer system (3-4 lb pressure I think). and a pressure regulator would be a good thing too. Dennis
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That happened to me in my 1973 VW Beetle.
The solution was to increase the fuel pump pressure. be careful when removing the fuel pump pushrod, or it might fall into the case.
Remove the pushrod first before removing the fuel pump block/flange.
You can get a good fuel pump pressure tester at Sears.
The next choice would be Advance Auto Parts.
They come with instructions.
The ideal fuel pump pressure for carbureted models should be from 3 to 5 psi.
Be carecareful and do not cause a fire.
The fuel pump pressure is adjusted by removing the shim gaskets, underneath the fuel pump. Test the pressure. Remove a shim and replace the pump. Test the pressure. Repeat if necesary.
Ahhh, summer, and bugs with problems with gas,,, every year! Jan or John H should do a web page about it!
Heres what I've learned over the years. Yes, the gas can get hot! Now, find out what is making it hot! Trace the fuel line where it comes out of the tunnel, and goes through the fire wall, and into the engine compartment. Make sure that the metal line is not touching the heater boxes under the car. When it enters the engine compartment, make sure its not touching the intake manifold, or the spark plug wires. Next, check the fuel pump. Pull it off, and make sure there is a gob a grease under the plastic spacer. The grease is insulation! Then, after all that, make sure your timing is correct as bad timing can also cause your car to overheat!
Hope it helps!
OK...
This is going to sound like a real stupid question, but how do you check the pressure of the fuel pump, if you have disconnected the fuel line? The car can't run with out the fuel line hooked up.
I'm sorry, I don't want to seem dumb, but please...
Thank you.
Car isn't running during pressure check. You put a pressure gauge on the outlet side of the pump. Have someone turn the car over (coil wire detached, you don't want the car running) and watch the pressure on the gauge.
turn over as with the starter?
I knew it,,, someone would ask that.... No, I don't mean we get Shaggie to literally roll (turn) the car over, yes, you just turn it over with the starter....
Thank you...
Man, do I feel dumb!
Thanks again!
On Tue, 27 Jul 2004 10:46:41 -0700, vwluvrs ran around screaming and yelling:
if you want an *accurate* reading it is necessary to plumb a tee fitting with guage into the line and *run* the engine...mechanical pumps tend to build a bit of pressure at speed...without the engine running you can't even get an accurate reading.. JT
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