<VV> Self pity and whining

[Frank DuVal]

norman.Witte at comcast.net wrote:

>
>Anyway, tonight I came home from work, grabbed the convertible, and went back to the office to get some work done.  Last fall the car had this problem where if you drove it for awhile and then parked it for a short time, it would start, but then sputter to a stop. 
>

Classic vapor lock.

> Then you could crank it and it would act like it was going to start, but it wouldn't stay running.  Then, suddenly, it would fire and run.  Over the winter the carb was rebuilt and I thought this problem was licked.  
>  
>
.
Carb rebuilding should have no effect on vapor lock.  Carbs use liquid 
gasoline to flow through the orifices until it atomizes in the venturi. 
Vapor does not flow properly in a carb.

>I was wrong.  I drove from the office to church to pick up my son from youth group.  In a repeat of the one other time I used it to pick him up from youth group, we got about half a mile and the dang thing died on me.  My wife came and picked us up and the car is sitting in a parking lot.  
>
>I can't for the life of me figure out what is wrong.  It seems to be getting some spark, because it will briefly catch and stutter.  I don't think the Pertronix is bad because I can't see how that would relate to shutting the car down.  I think its not getting enough gas because I can pump the accelerator heavily, and it doesn't flood, it just does the same sputtery thing.  I thought about vapor lock--I don't know much about it--but I thought that required hot weather, and tonight it was fairly mild, maybe in the upper sixties.  
>  
>

The temperature needs to be high enough to boil the liquid fuel. Tony U. 
mentioned winter blends still being in your tank. This winter fuel boils 
at a lower temperature.

The other BIG clue is the "hot soak" period required to cause the 
problem, hence the "classic vapor lock" symptoms. When you park the car, 
the engine is warm and the fan is nolonger cooling the engine, so the 
temperature of the engine compartment rises because the engine is warm. 
This heat gets into the fuel especially in the fuel pump as it is 
physically connected to the engine and a thermal path exists. So if you 
kept driving, the fan would keep the fuel cool. If you parked longer, 
the heat would dissapate through the body sheet metal and other paths 
(convection, radiation) thus the fuel would again be cooler and 
therefore a liquid.

Electronic components can also exihibit a hot soak condition as some are 
susectable to heat problems when they are defective.

A fuel pump can pump vapor, but the quantity of vapor available from 
boiling fuel is way  more than the pump can handle. I mean say 1 cc of 
liquid fuel when vaporized occupies way more than 1cc of volume. And the 
pump is pulling a vacuum on its suction side, so the pressure is lower 
and the liquid boils into a vapor at a lower temperature than on the 
pressure side. Too technical now?

The roadside cure for vapor lock is to pour your iced drink on the fuel 
pump and input line to the fuel pump. Once the vapor is condensed back 
into a liquid in the pump, great volumes of liquid fuel can be pumped 
through the vaporized line and carb to get liquid fuel to the carb 
passages and it will start and run.

The carb fuel bowl usually does not run dry during a hot soak period, 
which is why the car starts and runs until the bowl goes dry of liquid 
and just has vapor in it.

If ice cubes on the fuel pump make the car start, then it is vapor lock.

Frank DuVal