Hi Steve,
I have never experienced signs of vapor lock on a very similar car. I
even have a metal can filter in the vertical pipe section.
In general, fuel that is under pressure, such as from the fuel pump
forward, is harder to vaporize & thus vapor lock.
Vapor lock symptoms are sometimes caused by a tiny leak on the suction
side of the pump. This could be at the pump inlet connection, at the
tank connection, or even in the internal tank down tube. The leak allows
air to be drawn into the pump but is small enough that fuel does not
leak out. Another possibility is that the pump itself is failing when it
gets hot.
Blocked or partially blocked carb float bowl vents could also cause a
similar problem.
When the car exhibits the symptoms, crack a fuel connection at a carb &
see if fuel or vapor is coming out, or neither.
Regards,
Dave Russell
BN2
Steve B. Gerow wrote:
> Pete Roses and I have been troubleshooting Sarah Frost's frame-off
> 100M for a whole-engine miss problem at running temperature.
>
> When the car reaches 190, it starts to miss seriously as if the whole
> engine is going on and off. Otherwise the car runs perfectly with no
> apparent richness or backfiring. The spark plugs are normal. 190
> seems a little hot, but the miss seems inappropriate for only 190--my
> car's run fine at 205 or even 212.
>
> Everything on the car is new or rebuilt, and we've replaced the coil,
> condenser and fuel pump as well as checked the fuel system for
> cleanliness--it's new and spotless. At no point is the fuel line very
> close to the exhaust. The closest point is the metal vertical
> up-tube to the front carb which is several inches from the manifold.
> Everything looks completely normal.
>
> My question--is it possible for these cars to vapor lock under normal
> driving circumstances?
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