> Subject: Effect of heat on fuel delivery
>
> Compliments of the season, all.
>
> This is a small but irksome issue: For about 20 to 60 minutes
> after parking the car when it's quite hot, restarting it is a
> real beast of a job...seems like fuel starvation.
>
> Let it cool for more than an hour and it starts great... or don't
> let it sit at all but restart it within a couple of minutes and
> that works too. But leave it for a middling amount of time
> when it's up to temperature and experience an embarrassing amount
> of cranking and pumping when you try to start it again.
>
I don't know what type of car you have, but I have had a similar problem
with my Spitfire 1500. Over a period of about 2 years, if I drove the
car for more than 1/2 hour at a time, the car would die. At first, I
let it set (usually 1 to 2 hours) before I could get it restarted. I
checked everything - fuel lines, pump, carb, etc. Couldn't find anything
wrong. Next when it continued to happen, I pulled the fuel supply line
from the fuel pump and found it dry - I thought either I was getting
vapor lock, or I had a faulty fuel pump. I guessed the former because
everything ran great most of the time.
It turned out I was wrong on both accounts. One day to pass the time, I
was reading through the shop manual (I was really getting frustrated
with this problem) looking at all the evaporative control stuff. I finally
found the problem. The spit has a sealed gas tank with a vent leading
up to the charcoal canister. In the line leading to the canister is a
little brass piece with a hole about the size of a sewing needle. When
you fill the tank this restriction prevents you from putting in so
much that you get gas in the breather line and into the canister. When
you drive, the hole lets enough air into the tank to replace the gas
being removed by the pump. That is, unless that hole is plugged (as
it was in my case, with lots of corrosion). If the hole is plugged,
as your pump extracts gas from the tank a vacuum begins to form in the
tank. This vacuum increases until the fuel pump can no longer overcome
the vacuum, and no gas then flows. By letting the car set, the vacuum
would slowly decrease until the pressure inside the tank returned to
1 atmosphere.
I cleaned the piece, and haven't had a problem since. To check if
this is the problem, simply open the gas cap. If you hear a rush of
air, and the car starts fairly quickly (give it enough time to refill
the fuel line between the tank and the pump) then I would check this
piece. It is located in the breather line right near the charcoal
canister.
--
Robert Palmer, Jr. Purdue University
palmerr@ecn.purdue.edu 317-494-3750
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