By Cliff Murray
If you are having engine popping problems in a car that has been modified to use an electric fuel pump exclusively (no mechanical pump), first try locating your pressure regulator close to the carbs, and if that does not work then change to a rotary vane type pump if you have been using a pulse type. Here's my story:
After having no luck tuning my 1883 with Solexes bored to 44mm/35.5mm for street use, I switched to Weber 44IDFs. Better but not great and the inconsistency of operation continued. Repeated ignition diagnosis and parts swapping bore no solution. Every jet combo you can think of without any improvement. Popping from the carbs (lean) and popping from the exhaust (rich) could occur at any time but never during wide open throttle. Sometimes I made a change and the car would run well (success?) only to have it revert to popping again.
During this ordeal I had a Pierburg 6 volt pump fail and that was replaced by the supplier by an Airtex 6 volt E8011 pulse type pump with pressure regulator. I do not remember any drive-ability change when I changed pumps. I do not use any mechanical pump so the electric pump runs all the time. I had checked the fuel pressure and volume on both pumps when installed.
Although there was no evidence that the second pump was a problem, I decided to change to a Carter rotary vane type pump just for kicks. I checked the pressure and noted that the reading was very stable. The previous pulse pump was very stable but there was a slight trace of the pump pulses. Not so with the rotary type. Success! The car has run the last 150 miles without a hitch and now reacts predictably to jetting changes.
I am guessing that the pulsing was disturbing the float level. I am also guessing that the location of the regulator, up front with the pump, is a problem especially with the unstable pressure pulses. According to Holley and others the regulator will respond more accurately when it is placed close to the carburetor. My regulator is still up front but I plan to move it to the engine compartment.
So, if you are having driveability problems with a car that has an electric fuel pump, first try to put your regulator close to the carbs and if that does not work then change to a rotary vane type pump.
If your only use of the electric pump is to fill the float bowls before driving, a pulse type pump will be fine.