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MG MG Y Type - Is this consistent with oncoming vapour lock?

Weather has a way of turning on a dime here. It snowed 6 days ago. Today, it was 80 degrees Farenheit.

So I took out the Y and drove a couple of hours in that unusual heat. Near the end of the drive, I stopped for 10 minutes at a doughnut shop for a quick celebration.

When I turned the ignition key back on, I heard the fuel pump clicking like a machine gun. I nonetheless started the car and the engine quit after a few seconds. I restarted it and it seemed to have a little bit of difficulty getting its fuel. After a little while, everything was back to normal, but I was still hearing the fuel pump racing once in a while.

I recalled a somewhat similar experience in EXACTLY the same circumstances a few years ago. I had a 1936 Ford V-8, the fuel tank was full of "winter blend gasoline" (because it was early Spring) and we were having a heat wave. The engine died because of the heat. And when I poured cold water on the fuel pump, it started back up.

"Winter blend gasoline" is sold in Canada from November to the end of April. Its particularity is that it is less dense than regular summer gasoline. Hence, it does not freeze up in the fuel lines and vapourizes much easier when it's minus 40 degrees.

On the Y, I do have a heat shield between the carbureter and the exhaust manifold. The cooling system works perfectly, but still, it was darn hot under that bonnet this afternoon. And the car is painted black and was sitting in the sun.

I will let it cool down and re-test the fuel pump tomorrow morning. But in the meantime, doctors, what do you think about these symptoms?
Gilles Bachand

Yes, you are suffering vapour lock or fuel evaporation.

In my experience there is little you can do about it with the car in standard configuration (and yes I have tried heat shields on carb and fuel pump), but when we stop like you did after a drive, we open the Right side of the bonnet & let all the heat out.

After the donut stop, you then close the bonnet & drive away. When the car stops moving the heat soak under the bonnet is impressive.

In Australia, the fuel blend is varied every six weeks, and modern fuels are so full of volatiles, that evaporation is common on old cars that do not have "sealed" fuel systems.

Just manage the problem as we do, don't try & remedy a problem created by the evolution of our fuels.

Happy Y-Typing
Tony Slattery

I had similar problems, but having had a heat shield made to the design specified in the Data Sheet (except that I used a slightly denser grade of aluminum than suggested which gives better heat conductivity, and the fitting of an insulation block (MG Midget/AH Sprite fit nicely) and longer bolts, it all works very nicely now and no more problems.

Paul
Paul Barrow

Many years ago I had a similar occurance in my YA near the top of a steep French Alpine Pass at about 10,000ft in blistering hot sun. By pouring water over the pump and fuel pipe the problem was overcome. I suggest a small water spray container would be useful. In my opinion the pump is mounted in the wrong place near the manifold and along with the new volatile fuels is bound to cause vapour lock problems. My pump is now mounted on the left side of the engine and much lower down.
Bryan

I never realised that North Yorkshire had so much in (weather) common with Australia, but the bonnet opening scenario is often a needed addition to fueling/feeeding/short stops.

If you experience the shudder of impending vapour lock try a little choke - I usually need to do so after re-fueling during long hot runs (and long cold runs as well!) After a few seconds push in the choke and you will be running OK.
Andrew
Andrew Coulson

Thank you for all your suggestions. I have done 3 new things to improve the situation:

1) Beefed up the previously too small heat deflector behind the fuel bowl and carburetter.

2) Insulated the fuel line as it comes up the firewall to the fuel pump. I theorize that this must help inasmuch as heat transfer to the copper tubing is slowed down a little bit, thus giving a better chance to the incoming cooler gasoline to keep the tubing at a more reasonable temperature.

3) Opened the bonnet in order to let the heat build-up escape when stopping for a while before resuming my trip.

I have noted the use of the choke unpon start-up, if need be, and will add that procedure the next time.

Today was sunny, very warm, my tank was full of winter-blend fuel (which the service stations will not start to replace by summer-blend gasoline for another few weeks) and I drove a good distance at a good rate of speed and with a full complement of passengers.

The result: There were just a couple of times when the fuel pumped clicked slightly faster than normal, but nothing approaching the machine gun rate of 3 days ago. The fuel bowl was much less hot to the touch. Start-up was straight-forward.

See attached photograph.

Gilles Bachand

This thread was discussed between 17/04/2008 and 20/04/2008

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