Fuel pressure at carb to High

GSW38 · January 24th, 2006

I have a 1938 Buick special. The fuel pressure at the carb is between 61/2 and 7psi.This high fuel pressure is forcing gas past the needle valve and causing too much gas into the engine.The result my spark plugs are being fouled.How can I easly regulate the fuel pressure down?
Thanks George

carbking · January 24th, 2006

If you are using a stock type fuel pump, kit it with the proper diaphragm return spring.

If you are using an electric pump, replace it with a low pressure SELF-REGULATED electric pump. There are many available.

Resist the temptation to purchase one of the dial type fuel pressure regulators (unless you have a strong right arm, and a rabbit problem in your garden).

You might also verify that the tank vent is operable. A clogged tank vent could allow pressure from heat expansion to overdrive the float.

Also, if you have a Marvel carburetor, replace it with the Stromberg. The Marvel on its best day was good for maybe 1 psi.

Jon.

GSW38 · January 25th, 2006

JON MY 38 HAS A STROMBERG AVV-1 ON IT. THE FUEL PUMP WAS REBUILT WITH A KIT FROM A REPUTABLE PARTS DEALER.
THANKS GEORGE

January 25th, 2006

your carb. needle valve is bad, or the brass "seat" screwed into the alumium housing is lose.

or your flows is bad.

it's not the fuel pump.

carbking · January 25th, 2006

George - the Stromberg AAV-1 should accomodate from 3 1/2 to 4 1/2 psi (maximum based on the mechanical advantage of the float). Stromberg specifies a maximum of 3 psi, but with a neopreme fuel valve the float should hold 3 1/2 to 4 1/2. More than that and you will get the results your are having. How about the tank vent? Is it possible it is clogged? The original pump should not put out the type pressure you report if it has correct parts. Either the pump has too strong a return spring, or something else is causing the excess pressure.

Jon.

JT · January 25th, 2006

I was having the same problem on my Packard with a rebuilt Stromberg EE-16 (neopreme valve)and rebuild fuel pump (running 4 1/2 psi). Changed the needle and seat but still had a problem. I then cut pressure back to 3 psi after checking specs on carb and have not had a problem since.
I was puzzled why the fuel pump spec was 4.5 psi and the carb spec was 3 psi for my car?

GSW38 · January 26th, 2006

I CHECKED TANK LEFT THE CAP OFF FUEL PRESSURE STILL JUST AS HIGH.SHOULD I PUT THE OLD RETURN SPRING BACK INTO THE FUEL PUMP AND CHECK THE FUEL PRESSURE?
GEORGE

carbking · January 26th, 2006

George - if you have the old spring, that would be an excellent test. Also, does the pressure immediately go to the 6.5~7 pounds when you start the car; or does it take awhile? Wondering if the fuel line could be too close to a heat source, and the heat causing extra pressure in the line?

Jon.

GSW38 · January 27th, 2006

Jon I appreciate your help.Jon I live in western Pennsylvania the temperature is in the 20's the fuel line is ice cold to the touch.The high fuel pressure is very noticeable at about half speed (61/2 to 7). If I run the engine at half peddle for a short time gas will leak out between where the air horn and carb body scew together. If I look down the carb as it is running at half speed there is a noticable increase in gas entering the engine as the pressure increases.
Thanks again
George

JT · January 27th, 2006

George, how is the pressure and fuel problem at idle? Did you check diaphragm spring? The wrong one could be a source of your high pressure.