View Full Version : mechanical fule pump ?

05-12-2006, 07:24 AM
I have a holley mech fp and have a 0-15 pres gauge on the line before it hits the 750vs. What i am wondering is when the engine is running and looking at the gauge it continuously fluctuates between 5,9,5,9,5,9, as in pressure. Is this due to the mech action of the mech fule pump or would it be something else or is it normal in mech fuel pumps?

05-12-2006, 03:10 PM
My pressure mechanical fuel pressure gauge with a mechanical fuel pump does not fluctuate at all as you described.

It could be the fuel pump not operating smoothly and pulsing. It could also be the needle/seat with the fuel pump over-presurrizing the needle/seat and loading extra fuel into the carb as the fuel pressure is released. Does the carburetor have any idle problems? Third thing is the gauge. Cheap gauge/quality gauge?

Most likely it's the pump pulsing. Just some ideas to consider.

Rick Dorion
05-13-2006, 05:13 AM
I believe it's the pulsing from the pump. The better gauges are damped to eliminate/minimize this.

05-30-2006, 10:47 AM
My gauge used to fluctuate like that when running a separate fuel pressure regulator with a return line. I don't think the regulator was a good match for the capacity of the electric pump I was running at the time. I could adjust the regulator to a point where the guage needle would bounce as the regulator valve opened and closed repeatedly, or back off the the adjustment and the regulator wouldn't open at all.

Anyhow, I mention this because I wonder if whatever regulator you may have, internal to the pump or otherwise, is causing the fluctuation in pressure.

06-27-2006, 06:10 PM
I have the same problem, I am using a good gauge I think.
Barry Grant Guage
Speed Demon 650 carb.

I had a BG HR220 electric fuel pump and the gauge was smooth.
When I switched to the mech. pump, the gauge bounces all over, and actually after about 2-3 minutes ideling in the garage I loose all pressure and the engines dies.

I am wondering if the mech pump is bad.

I switched from the Electric to the mech, because I thought it was overheating but I don't think it really was now.