Fuel pressure

When I opened my fuel tank the bottom had about 1/4 to 3/8 inch of crud like varnish built up.It had plugged the suction line up thru the top of the tank. I have not been able to clean it so I plan to replace it. I used 3 gallons of water and three pounds of dry ice in the tank. This made enough carbon dioxide to keep any flame from my torch causing an explosion. Then after removing all the soldiered parts I had the tank cleaned. Its ready for Cad plating now. Varnish is difficult to remove with whats available today. We can't buy the 1 gallon cans with the strainers in them for soaking carb parts...


Gary Parsons

Gasoline will turn to varnish and clog passages. Take the inlet line and try to blow compressed air thru to the tank, you will feel resistance if there is a varnish build-up, Sometimes squirting carb cleaner reversed top tank will melt it and you can get improved pressure, at least you will know it has hardening of the arteries. difficult to remove like paint.

Thanks all for your answers.

I removed the mechanical pump, there was some wear and play inside that I was able to correct. The membrane was new.
My car is also equipped with an electric fuel pump near the tank, but pushing only at 1.5 psi and 40 liters per hour, but through the mechanical pump.
If I have now nearly 2PSI, the debit is really low and I am still missing fuel at high revs.

Any information on the ideal length of the push rod ?

Many thanks

Thierry

You should have 2 to 3 psi at the carb. Any more then that the needle can't hold the pressure and you will flood the carb.

There may be problems in the fuel pump but there is a good Chance the push rod for the fuel pump is worn. This was a common problem which results is short strokes for the pump and not enough fuel to the carb at higher speeds. THe easy solution used to be caps that could be placed on the end of the push rod to lengthen it. I haven't seen these in years (altho I think the Ford gusy have them). THe modern way is to weld the end of the push rod and grind it flat to add some length.

I have a sneaky little electric one underneath to supplement the lift pump if required, great for priming after standing for a while.

Thierry I think 7psi is too high, low pressure electric fuel pumps which are also used on these cars only put out 3 to 4 psi and work well with that.
I am not sure where you can obtain a rebuild kit for the fuel pump.
Try Auburn Cord Parts in Kansas.

Not sure about what pressure we need. But you may need to rebuild your mechanical pump. Also the pump mechanical piston that works off the cam may need to me lengthened so the pump can make more pressure and volume to the carburetor.


Gary Parsons

Hello,

On my 1937 812, the engine is not able to go over 2500 rev when driving, seems missing fuel.
I managed to measure the fuel pressure at the carb, and I have no more than 1 PSI.
I red somewhere that 7 PSI are needed. Can someone confirm ?

Are the mechanical fuel pump easy to find and where can I find them ?
Or maybe can I just change the membrane inside ?

Many thanks

Thierry