Fuel feed mystery

[RotoFlexible]

Trying to figure out what just happened...

A hot day here in New England. I made a couple of stops, got stuck in a couple of five-minute waits to make a left turn. Engine was getting toward 90C, but no higher. After the second left-turn wait, I got classic fuel starvation symptoms - then it seemed to clear - then fuel starvation again and the engine died. (This with my 4-1/2 year old granddaughter along.) My first thought was some sort of vapor lock.

I determined that there was no fuel in the carburetor bowls. The electric fuel pump in the boot was running but I couldn't see fuel moving through the filter. I bypassed the filter - no joy (and the filter didn't seem clogged anyway). The pump seemed very hot and I thought it might not be pumping even though it was making noise, so I patched in a spare pump. Still no joy - no fuel to the carbs. I blew through the line from the boot to the front - seemed clear. Finally, in desperation, I opened the fuel filler cap in case there was a vacuum in the tank. This time, I got fuel flow, the car started and I got it (and my granddaughter) home.

I am not 100% sure that opening the filler "fixed" the problem. However, most of the fuel system is new - 5/16" steel tube running through the spine, with new fuel-approved rubber hose in the boot and the engine bay. I don't completely understand vapor lock, but I would think that it would be an issue if I had the original mechanical pump in the front sucking fuel through the spine, but not with an electric pump in the back.

It's possible that the fuel pickup in the tank is partially clogged - I can try blowing through it to force any clog back into the tank. As far as tank venting is concerned - I don't know how it works and why it would fail now. I can try driving with the filler closed to see if the problem recurs...

Any suggestions as to what may have happened, how to diagnose it, and how to keep it from happening again? I have a Carter pump drawing fuel through a filter, a dial-type regulator also in the boot, and the aforementioned plumbing to the carburetors.

[1964 S1]

How many gallons of gas were in the tank? Was there a whooshing sound when you removed the fuel filler cap?

[neilsjuke]

Could any silicone sealant used in the past be in the tank it swells up in petrol .
Neil

[RotoFlexible]

The tank was about 1/3 full. I had opened and closed the cap at least once during the diagnosis process (before I got it running) and didn't notice a woosh, but is was a very noisy environment. I think the closed filler may have contributed to, but not caused the problem.

I did use a very light coating of silicone sealer on the sender gasket (I learned the hard way about using too much a long time ago). The tank was professionally flushed and internally sealed before I replaced the sender. That was last year and 3,000 miles ago and I've had no trouble with the fuel system until yesterday. The one new factor is the opportunity for heat buildup.

[twincamman]

Just had this problem with the Europa -----there was shmidt in the tank bottom that would jam the filter solid ----changed filter 4 times and finally pressurised the tank to empty it -----most likely I picked up a load of crud from my friendly gas purveyor ----drain the tank under a light pressure from your compressor into a transparent container --change the filter --and clean out the brass filter on webers -----the other solution may be your tank is not venting and the vacuum in the tank is overcoming the fuel pump pressure ---------good luck IM off to carve up some curves before officer Bob gets up --- ------ed

[dlbarnes1]

Check the vent hole on the filler cap.
Dave 72 Sprint DHC

[RotoFlexible]

I don't have much of a resolution for this problem. I put everything back together the way it was (with a new filter) and of course it runs just fine. I tried the "suck it and see" approach to the supply line from the tank and was rewarded with a taste of high-test (not my intention!). The line from the boot to the carburetors seems clear. The vent hole in the filler cap seems clear. The tank itself should be free of debris.

It remains a mystery.

[denicholls2]

My vote is for a venting problem as well.

The amount of gas you start with matters, because we're talking about an air seal here. If the tank empty volume increases greatly in a short period of time (say, by starting with a full tank and going on a long drive), then pressure will have a lot less time to equalize through poor venting (which if left overnight would likely correct itself because an air-tight seal is not easy to maintain -- reference drooping headlight issues ).

Air does need to get in to replace fuel burned, and gravity alone does not guarantee that result.