Vapour lock - how to solve?

[Robert Deutman]

Dear all,

My 356 keeps having (suspected) vapour lock issues despite having tried the following:
1. Use of 102 octane fuel without ethanol;
2. Installation of Al Zim electrical fuel pump under the fuel tank (away from heat);
3. Installation of heat-isolation “socks” over incoming fuel pipe (the one that ends at the mechanical fuel pump);
4. Refurbishment of carburetors;
5. Application of ice/water on the mechanical fuel pump (this does seem to shorten the time before the car restarts);
6. Check that fuel lines aren’t making any metal-metal contact with engine components.

The problem occurs when the engine is hot (just outside the red zone) and the ambient temperature is 25-30 degree Celcius (77-86 F). The car runs perfectly when cold and runs very well for an hour or more at the highway. As soon as I come off the highway (e.g. to stop at a traffic light) the engine stalls and won’t start until after a complete cool-down.

What can I try next?
A. Heat insolate all fuel pipes/hoses in the engine compartment?
B. By-pass the mechanical fuel pump (is the pump chamber where the fuel bubbles start?) and run on electrical pump only?
C. Install better cooling of the engine (replace cooling fan or install extra electrical cooling)?
D. Reroute fuel pipes (problem: I don’t know where the current “hot spots” are that are causing the issue)?

Does anyone have any ideas or experience? The car is otherwise driving like a dream.

Thanks,

Robert.

[C J Murray]

Are you still using a mechanical pump? The early style pump is prone to vapor lock.

Why is the engine running so hot? Do you have the ignition timing and jetting set correctly? Do you have a severe detonation problem that even the 102 fuel doesn't cure? Does it ever ping?

[George Walling]

Robert, I would suggest checking your timing, if you are running a electric fuel pump and have it mounted where it is pushing the fuel instead of pulling the fuel as a mechanical fuel pump does you should not have a vapor locking problem. Back in the day we would mount are electric fuel pump as close to the fuel tank as possible to solve are vapor locking problems. I use a clear fuel filter in my 55 speedster and when using ethanol fuel I had the vapor locking problem and the clear fuel filter allowed me the chance to see the fuel boiling in the filter between the pump and carbs. I'm running the non ethanol fuel now have solved my problem. So with everything you have tried and have not solved it I would get a clear fuel filter and see if the fuel is boiling in the metal fuel line. also check make sure your fuel pump is not putting out more than 2.5 to 3 lbs pressure. I have run my speedster here at 4500 ft elevation and never had any problem when outside temp was below the 90's so I think you maybe have another issue than vapor locking. Good luck.

[Thomas Sottile]

You can buy some foam AC tubing insulation from a AC supply house with a diameter that will work, then cover the fuel lines in the engine compartment.

[Greg Scallon]

Robert,
Maybe it's not a vapor lock problem after all. Have you checked your valve adjustment lately? I had a problem once where the valves were too tight, such that once the engine was nice and hot, they would expand and not close completely. The engine would behave much as you describe. It would start fine when cold, run even while hot, but there's no way I could get it started again if I stopped it while hot. Once it cooled down it was fine again.

Just something to consider. Good luck with your mystery. Hopefully you'll solve it soon.

-Greg

[David Jones]

Greg has a good point. There are thousands of 356's out there that do not have vapor locking problems and only a few that have overheating problems. I suggest a complete tune up before trying to solve a problem that does not exist. Go buy an IR gun and start checking temps. In particular check the oil filter temp and the temperature at the temp sender. If the sender temp is less than 220 when the temp gauge in the car is close to the red then you are probably not overheating. Oil temp at the filter I have rarely seen over 200*F.

[C J Murray]

Aluminum pushrods with iron cylinders can cause the valves to hang open when hot.

[GregVandenbussche]

1/2" phenolic spacers under the carbs might help

[Leo Dreisilker]

Midwest 356 Club had a drive to Wisconsin today in very hot weather. It was 95 F and after an hour of driving to the meeting point I stopped for gas. After filling it up my 62 B Coupe took a long time to start up. After driving a few blocks to the meeting point I checked temps with a hand held laser temperature gun. Temps at several areas on the case were in the 175 to 185 range. The temp gauge in the car was at the 3/4 level. On the way home running for 2 hours around 75 to 80 mph the temp gauge was in the white. Checking temps again showed nothing over 200 F. Why is the temp gauge showing a very hot temp? Could there be a calibration issue? I do know the heat deflector is missing and will be installed next Tuesday. At our picnic we discussed flooded carbs as others have experienced similar issues in the past. My car did not do this in the past and the valve adjustment issue has me wondering as the shop adjusted the valves last year. Any advice would be appreciated.

[Robert Deutman]

Many thanks for the responses. I have some new leads to follow up on!

[Tom Wavrin]

Robert, I solved my car's 'vapor lock' problem by resurfacing the brass seats for the 2 flutter valves in the fuel pump. Tom

[Ronald Jones]

I had a similar problem with what I called "heat soak" with the Zenith carbs on my
65C. When stopping after a long run on the interstate, the car would not start
unless it sat for at least 1/2 hour. I installed phenolic spacers under the carbs, problem solved.
Purchased a square of the material from Sportys Pilot shop in Ohio and made my own spacers,
they were not 1/2 inch thick, more like 1/4 inch.

[David Jones]

For those without access to a machine shop or tools to make spacers.
http://willhoit-auto-restoration.mybigc ... lator-kit/

[Mike Horton]

For those running the Solex 40 PII. and the two piece side vertical tins, be sure they are not the one year only '68 "smog pump" tins, as the access hole for the steel air plumbing, if not filled, when the air pump was "legally" removed, will allow the pre-heated air, after it passes through the heat exchanger (oil cooler), to be directed right at the left side carb base, and intake manifold, thus...vapor lock, on ethanol fuels, and Hot TX summer weather, at short stops, when the hot components will accelerate the higher evaporation rate ( I read everything David Jones writes), Thanks, David, back at the change from "real gasoline" to the PC 10% ethanol, this cause nearly drove me nuts... I discovered this tuning the split shaft driver's side carb, after the engine was up to normal temp. Also on the '68/'69 912 engines, swap out the steel carb spacers, to the phenolic versions, as on the S90/SC/& through '67 912.

The root cause, is where you find it!