Mechanical Fuel Pump Pressure Adjustable?

[TobyB]

I had success with the bypass using a Holley Red pump with DCOE's- the pump

had both a ton of volume and and the ability to build real pressure against a

dead head.  So letting 3/16" x 3/4" of fuel flow bypass the carbs

reduced static head pressure enough to not flood the carbs at idle or overrun,

and still keep the bowls full on a long straight.

 

 

[John76]

Thanks for the suggestion on a bypass. It worked!

I installed a "T" on the fuel line from the pump to the return valve, and used a small valve to regulate the flow into a gas can.

 

I opened the valve until I had the 2 psi to the carb. This is with manifold vacuum to the fuel return valve.

 

When I disconnected the vacuum to the return valve, the pressure to the carb increased to 3.5 psi.

 

Results:  Hummm....didn't see a difference in the smoothness of the idle. This was my goal, as I thought the Weber was unhappy with 3.5 psi.

I did not do an actual road test since I would need proper fittings and hoses (heat and gas proof), and plumb the bypass hose to the return line to the tank (downside of the check valve).

Also, the volume of gas bypassing the fuel return valve (about a quart in 5 minutes) caused concern about running the float bowl dry at extended  part-throttle cruise speeds. WOT would get 3.5 psi to the carb (for a quick refill of the bowl).

 

So, thanks for all your feedback and suggestions. It was fun to see the results of this test.  The elegant solution would have been to weaken the spring in the Pierburg...but this is not serviceable.

 

This last picture was taken just before the explosion and fire  .