Rob describes a problem with his Bug that really had him going for a while -
I'm usually quite good at diagnosing problems with VW Beetles, but this one has me flumoxed, so I'm looking for inspiration.
My Bug is a '68 semi-auto, converted to manual, with '71 1600tp engine, 30PICT/3 carb and single vacuum distributor. The car still has its solid '68 engine lid (no slots - slotted lid coming before winter in Australia ends). I bought this car about 5-6 weeks ago, from a PO who shouldn't be let loose anywhere near VWs, though he's had them for years.
The problem appears to be fuel delivery.
Symptoms -
The car runs for about 5-6 miles before the fuel stops flowing - float bowl and fuel filter empty out. The fuel filter is currently between pump and carby, so I can see if the pump is delivering fuel. Wait for 5 minutes or so, and crank for a while, and the fuel starts flowing (visible in the filter) and he starts, and he's right for another 5-6 miles (a lot longer than a single float bowl full of fuel).
These problems happened just a few times when I first bought him (before I replaced the perished fuel lines), then stopped, and just recently started again, this time worse.
History -
The car had a PO who ignored his VW ownership responsibilities, so in the last few weeks I have:
So - the problem occurs with the fuel cap on or off - it's not a tank vent problem.
Fuel flows freely out the pipe under the tank.
Fuel flows freely out the rear end of the steel body line - no blockage there.
Fuel flows freely into the carby under gravity flow.
All rubber lines are clamped - no possibility of air entry or fuel weeping.
I wondered if the fuel pump had something stuck under one of the two small valves inside which might be reducing flow (from the perished rubber fuel lines or crud from the tank), but replacing the pump produced no change at all.
I wondered about the fuel pump overheating (vapour lock), so tried pouring cold water on it after the problem occurred. This seemed to help (a few bubbles sometimes appeared in the upstream filter), but only occasionally, and the pump was only warm to touch. Same problem when I replaced the pump - no change. The steel fuel line around the left side of the engine is not near anything hot, and gets only warm to touch.
It's winter here in Australia, so temps are between 3-6 at night, and under 20 during the day. Engine heat doesn't appear to be a problem.
I'm stumped - anyone got any ideas - I'll listen to them all.
In his typical fashion, Rob resolved this problem himself -
The answer turned out to be the most simple thing - the $3 fuel filter!
Though it looked OK, and when I blew backwards though it I had no trouble blowing air through it, the thing was apparently partially blocked - enough that only a trickle of fuel could get through. So giving it a rest allowed what was in the pump to leak through and partly fill the bowl, then as I drove, the trickle was less than the fuel use and eventually the car conked out again.
Can you say "Doh!?"
I thought I was following my own philosophy - look for the simple things first, but I didn't think simple enough in this case - when the "blow through it" test worked on the filter, I didn't consider it again until I spoke to a mechanic friend.
The car ran home that night (from the shop where I replaced the filter) and to work this morning, without missing a beat.
Who'd a thunk it!
Only the Super Beetles have the fuel filter at the tank outlet. Standard Beetles had a mesh screen INSIDE the tank, as well as a filter inside the fuel pump (original style -- a later model, which has a lower profile to clear the larger diameter of the alternator, has no inbuilt filter). If it's the original type, the filter is behind a nut (about 13mm I think) on the side of the pump, just in front of the fan belt as it passes the pump body. This belt gets in the way a bit as you undo the filter plug. It's a fine plastic gause. If the pump has no nut in this position, you have the other type of pump without the filter.
The additional filter at the carb was an add-on but still a good idea.
Particles inside the fuel filter usually mean there is rust inside the fuel tank, and if this is true, it can get worse. In the Standard Beetles there is a fuel filter inside the tank too, when you pull the outlet fitting from the bottom of the tank the filter comes out - it's long and round like a pencil. You have to remove the fuel tank to get at the outlet underneath.
If the tank filter shows a lot of rusty flakes, then you need to clean you tank. See the Fuel Tank Removal and Refurbishment procedure on our main page.
John Connolly (Aircooled.Net) wrote regarding the filter between the fuel pump and the carburetor -
Install the fuel filter next to the transmission. You should NOT have a filter between the pump and carb. The added weight of the fuel in the filter at THIS location can wiggle the fuel fitting in the carb loose, and it will pop out spraying gasoline all over your hot engine AND THE DISTRIBUTOR (sparks + gasoline = empty wallet + tears + no more car). Don't say I didn't warn you!
Dave posed the following question to Rob -
What do you think about the fuel filter between the fuel pump and the carburetor? John Connolly recommends that there shouldn't be one there, others think it's a good idea. What's your opinion?
Rob responded -
John's main concern there seems to be that the weight of the filter may put additional strain on the brass inlet spigot in the top of the carby -- a known source of fires in VWs. Mine worked loose about 2 years ago, and I think I mentioned knurling the section which is pushed into the carby so it can't work loose again. The other concern I've seen is that if that filter got clogged, the pressure from the fuel pump might cause the fuel line to pop off the filter and spray fuel all over.
Both arguments have some merit, but are not overiding considerations. If your carby inlet is firm, the filter is not likely to pull on it much, and you can always arrange the filter so the weight doesn't pull on that spigot. And the fuel pressure is only 2-3 psi, so it doesn't take much to seal the fuel lines against that pressure - so that even a blocked filter would not cause it to pop off. The fuel pump design allows for this - the operating lever simply doesn't descend to touch the cam drive until fuel is used, so if the filter got blocked, the pump won't pump anyway.
If you had only one filter, I'd say put it before the pump, either in the engine bay or under the tank, but with two filters, one under the fuel tank and one between the fuel pump and the carburetor should be fine.
Disclaimer stuff: Rob and Dave have prepared this information from their own experiences. We have not assumed any specialised mechanical knowledge, but we DO assume that anyone using this information has at least some basic mechanical ability.
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Last revised 5 May 2004.