Tom :
I've never suffered true vapor lock either (every potential instance has
turned out to be something else), but my understanding is that it can be
used to explain almost any odd behavior <g>
Basically, the fuel starts boiling inside the fuel line, typically
between the fuel pump and the tank. Small bubbles of vapor will
eventually be passed by the fuel pump, but can temporarily interrupt
(liquid) fuel flow causing the engine to stutter and miss. Larger
bubbles of vapor will eventually cause the pump to quit pumping (they
don't deal with vapor very well) and the engine to die as though you are
out of gas.
The first step is to identify whether you have a fuel delivery problem,
or a spark problem. One way to do this is to carry a can of starting
fluid (available for a few $$ at any auto parts store) and when the
engine will no longer run, try squirting some into the air filters and
then immediately trying to start the engine. If it starts, runs for a
second and dies, then you are having a fuel starvation problem.
Another simple check on a TR3A is to try the priming lever on the fuel
pump. If you already had fuel pressure, then the problem is either at
the carbs (bad fuel line, crud in float valves, sticking valves, etc.)
or an ignition problem. Vapor lock should feel as though you are out of
gas.
You can also try pulling the hose off the pump inlet. If your gas tank
is fairly full, you should get fuel flowing freely out of the hose.
Vapor lock will probably produce visible vapor, followed by liquid fuel
(after the gasoline cools off the hot spot).
BTW, you didn't mention replacing the fuel hose from the shutoff valve
to the pump, or from the hard line to the front carb ...
Randall
59 TR3A daily driver
Tom Bottman wrote:
>
> OK, I've put off posting this question for 2 weeks, thinking that the
> problem could be caused by so many things, that an internet diagnosis
> would be asking too much. However, I' really stumped.
> Late last fall the TR3 began to misfire and stall after driving for at
> least 1/2 hour. The stalling starts out as a few misses, with the engine
> then returning to its normal great condition, this often progresses
> until I'm going nowhere but to the phone for the tow truck. I
> progressively replaced the fuel pump, the coil, the ignition wires, the
> low tension lead, the condenser, checked all electrical connections I
> can think of. Seems to occur more often and more drastically on a hill
> (whatever that is worth).
> My suspicion now is vapour lock. Since I have never been plagued with
> that particular ailment on any car before, I need to hear what the exact
> causes of this are, and if the symptoms fit.
> Thanks,
> Tom Bottman
> TR3A
> TR6
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