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Unless I keep pumping the accelerator pedal, the VW engine won’t stay running when left to idle or at a stop light, even after running for a while (30 minutes, at least). Could I have a weak fuel pump that is just not getting the fuel to the carburetor? The fuel line appears to be copper tubing. Should I consider replacing that with something else, maybe brake line hose?
It is unlikely that your copper line is causing the problem. You should replace it with hard fuel line anyway. Eastwood sells it by the roll along with bending and flaring tools. Harbor Freight sells the tools for less, a lot less. Don’t use brake hose.
Does the engine run normally at speed and under acceleration? If so the problem is in the idle circuit.
Does the engine idle with slight pressure on the gas pedal or do you have to pump the pedal to keep it running?
Pump? You could have trash in the idle jet. Drain and clean the sediment bowl. Run fuel conditioner for a couple of tanks. Removing and cleaning the carb comes next. Install/replace your fuel filter.
Slight pressure? The mechanical idle screw on the linkage at the carb could have backed out. Or the idle air screw needs to be adjusted. Or the idle fuel screw needs to be adjusted. It depends on the carb.
The recent cooler weather could have increased the density of the air in the cylinders, leaning out the mixture at idle.
You haven’t adjusted the valves recently and they are leaking at idle. Are they chuffing or clicking normally? Chuffing? Adjust the valves.
Have you changed anything recently? That new alternator could be adding load at idle. Adjust the idle.
If you haven’t changed anything and there are no new noises, I would start with the idle air screw.
Read “adjust idle” on page 116 of “The Volkswagen For The Compleat Idiot” by John Muir.
Take a look at “died with my slippers on” under this thread. I posted a problem I had that sounds very similar to yours. As long as I kept the engine revved up it would run okay, but as soon as I took my foot off the accelerator it stalled. It turned out to be a wire that pulled off the “Idle Cut-off Valve”. As soon as I re-connected it, the car ran fine. I posted a picture on there with an arrow showing where this valve is. I’m told that this valve could be on the opposite side on some carburetors. Check that out. It could be as simple as that.
So far we have reconnected a wire from the coil to the choke. I pumped the gas pedal once and she started right up. But after running for a minute or so, it seems that the choke warmed up and opened ?) limiting the fuel and it dies.
Did you look at the picture Paul posted? There’s a smaller barrel with a spade connection below the choke–could be on either side of the carb. Connect your + wire from the coil to that thing and try again. Dollars to donuts that’s your issue.
If not, then probably clogged idle jet–you need a small strand of stiff wire to poke it out.
All this assumes your sparks are in order–you static timed it to 4 before TDC already?
Quick way to check that Idle cut-off valve. Open engine compartment and have assistant turn ignition key to “ON” not start. When the key is turned on you should here that valve click. If you don’t hear the click, then its one of three things: 1) you don’t have the wire from the coil connected to open it, 2) you have a bad valve, or 3) you don’t have a valve. Some folks weren’t sure what it was so they removed it and put a plug in the port.
Allen Caron
VW based 53MGTD - "MoneyPenny"
"If one thing matters, everything matters" - from the book The ShackWhen the engine is cold the butterfly valve is closed so the car runs rich, and that also makes it easier to start. When the car is warm, or when the electric heating coil in the choke warms up, it opens the butterfly valve so the mixture is correct. Opening the valve lets in more air, it does not limit the amount of fuel.
If the engine runs well at speed on the road, it is not a problem with the fuel pump.
Are you using this car regularly or does it sit for a long time? How old is the gas? If your idle cut-off valve seems to be working OK, you could try putting
in some carb cleaner, like Seafoam or Berryman’s B12 Chemtool (better
and 1/3 the price) into the fuel 1-2oz/gal, no more, and run it for a while through at fast idle or whatever rpms you need to keep it running, and see if that cures the problem.
You may have to remove and clean the carb, maybe the idle jet is plugged.
Do you have a see-through plastic fuel filter? Anything in it you can see? Is it at least 1/2 full?
Does it idle really slow and then dies or does it just quit? You might try backing out the air screw a little, like a quarter turn or so (large screw on the side), to increase the idle speed just a tad. Sometimes a change in temp affects the carb adjustments.thanks for the advice. The car is now at a fiberglass repair place to spruce her up, fix the cracking, paint chips and bubbling. I had a window to get her to that shop yesterday, so I ran her over and left her.
These tips are wonderful. I’m going to print this out and start working on this as soon as I get her back from her facelift.
The engine slows down and dies after it ran for about a minute, then wouldn’t stay running each time I restarted it. We reconnected the wire from the coil to the choke and adjusted the choke, but it still isn’t helping.
She might sit for a few weeks at a time, but I try to start her up about once a week or two. The plastic fuel filter is less than half full.
Keep us posted on what the problem was. We offer advice based on our experience with a similar problem. There could be half a dozen reasons why your TD won’t idle when it warms up. We’d like to know which one it was.
Here’s an easy one. What does your air filter look like? Clean it or replace it before you start adjusting the carb. Restricted air flow could be enough to stop the engine at idle. Make sure that the hoses leading to the carb are clear too. Mice and birds can build nests faster than you would believe.
Lets check the plugs.pull al 4 and see what they look like,any evidence of fouling?A gas fouled plug will never fire correctly when at operating temp.
My neighbor towed her home from the fiberglass repair shop that was too expensive for me to consider, and once I got home this past Thursday, the engine started up and seemed to sound and run better. But it didn’t stay running and had to be restarted a few times, just to move it over in the driveway so we could pull the engine the next day.
I had a Land Rover with a similar problem. I drove it so little that the orifice in the bottom of the float chamber would grip the needle and pull it out of the float fork. It would allow a little fuel past the needle. I could drive for a minute or two on level ground but I’d eventually run out of fuel. Pressure in the line would fill the chamber after a while and I could drive again.
Pop the top of the carb and see if the float needle is hooked up to the float.
I don’t know what type of carb you have, but the Solex carb (mine’s a 34 PICT3) has the needle fixed into the valve on the top of the carb( by the inlet hose), not attached to the float – it simply rests on top of the float, going up and down (in and out) to close and open the gas flow as the float rises and falls. It’s very easy to get to, remove the 5 screws on the top of the carb, take off the spring attached to the throttle, remove the top of the carb and see if the needle valve slides up and down easily. If not, unscrew the assembly from the top of the carb, clean it with carb cleaner until it moves with no resistance and slides up and down with ease. If it is clean and working well, you should be able to blow air through the gas inlet if it is in the normal upright position, and not be able to blow through it if it is upside down and closed, or of the needle is pushed up. See that the float is free to move up and down. If all is well, put it back together and it should be good to go as far as that part of the carb is concerned.
Also, if you take the top off, make a note at what level the float is and if there is any gas in the bowl. If the float is down and no gas is in the bowl, maybe that valve was clogged and not letting gas into the carb. If the carb was full and the float is floating near the top, that may not be your problem, but you can easily see if it’s clean and working anyway.
If that’s OK, the problem may be a clogged idle jet. Find a diagram of your carb online and find the idle jet, take it out and clean it either with a very fine wire and/or carb cleaner and then blow it out.
Put some Seafoam or Berryman’s B12 Chemtool (better and 1/3 the price) into your gas tank, 1 oz/gal of gas, and as it runs through it will clean the carb also, and is a good preventative maintenance idea every 3 or 4 tankfuls, if you don’t drive the car much.I pulled the engine to have it totally rebuilt and enlarged to an 1835cc size. We found my valves burned but the rings were in good shape. Obvious heat damage, based on the blue coloring of the metal. I’m going to try for a dual carb set up with two new carbs. I’ve had trouble ever since the last one was put on.
We should have her back in running in a week or so with about twice the horsepower she had before.
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