Jarl,
Some good data on fuel pump capacity.
Bruno,
I would agree that we need to establish whether or not the problem is really
vapor lock. Vapor lock is a problem related to heat. It is when the gasoline
boils in the fuel line (or carburetter). The resulting vapor takes up all of
the space in the line (or carburetter bowl) until the temperature cools off
enough to let the fuel recondense to a liquid. Vapor lock is also aided by
low fuel pressure, if you've got a whimpy pump or clogged filters / screens.
This time of year (where are you located and what is the temperature?) vapor
lock would be unusual. My son's '76 Midget's previous owner said the car was
very prone to vapor lock. As we went through the car we found that the metal
fuel line brackets were not attached or missing and most of the metal line
and some of the hose rested on the side of the transmission and top of the
clutch housing. We replaced those brackets and got the fuel line onto the
body of the car and off of the hot running gear. We also replaced a leaky
mechanical fuel pump and the fuel filter. When the hot weather came, we never
saw a fuel problem.
Check the fuel line routing. Make sure its not laying on hot surfaces. Make
sure any heat shields are in place on the carburetter(s). Clean any screens
in fuel pumps / carburetters and replace filters. If you still are having
trouble, look for air leaks on the suction side of the fuel pump as Jarl
suggested. They can't be seen. Leaks on the pressure side will be much easier
to find. They drip.
One other thing to check would be the pickup tube and its screen in the gas
tank although there can be quite a lot or rust and the like in the tank
without having a problem. Unfortunately, the age of our cars can make this a
possibility. The easiest way to check is to disconnect the hose and blow
(with your mouth) back to the tank. There should be very little restriction
(take the gas cap off). If there is, the screen on the pickup tube might be
clogged up. If this is the case you'll have to drain and pull the tank off
and do some serious cleaning. This is a moderately difficult job and one to
be VERY careful doing. A well ventilated area is absolutely necessary,
preferably outside on a nice day.
I had a Japanese car that the screen (a sort of can shaped thing about the
size of a "D" cell) came loose from the pickup tube. The lack of the screen
wasn't yet causing a problem but, the damn thing would float around in the
gas tank and, every now and then, get its non preforated top sucked tight on
the end of the pickup tube, starving the fuel pump. The car would die, the
suction would equalize, the screen assembly would drop off. The car would
restart (after cranking a bit) and be fine until next time. It took me a few
months to fiquire that one out.
R. Johnson - Dallas
'90 Maine Coon
'79 Midget
'76 Midget
'73 MGB
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