Basic question about a vacuum fuel pump By trailheadmike (Read 1,168 times)

[trailheadmike]

I had a leaking fuel line recently. I had a second in-line filter near the carb that apparently cracked, and the fuel was just shooting out with the motor running.

It made me think - that was a lot of fuel coming out. I bet I could have emptied the tank in half an hour based on the flow. What happens under ordinary conditions? I mean, the carburetor couldn't possibly accept that much gas just for idling, but the pump is going at a certain minimum rate as long as the motor is running. Looking at the flow, I would think that the line would burst or the carb would be discharging gas under idle.

Forgive me if this is a foolish question, but I can't picture the answer.

Thanks in advance.

[Bashan]

There's a relief valve in there that bypasses excess pressure so nothing gets damaged. These pictures are from a guy called EarlWB, I'm not sure where he's knocking around now. Of course Photobucket scrambled the order when I uploaded them but you can kinda tell how it goes together. The important pics are the two that show the relief valve. Rich

[trailheadmike]

thanks very much. A picture is worth a thousand words. It seemed that the only place the pressure could find relief would be for the gas to go back through the pump the wrong way which did not make sense, but if I understand you that is exactly what happens via the relief valve.

Thanks again Bashan for this and all of your past very helpful posts. You're archived material has helped me time and again.

[jct842]

TRAIL, your thread concerns vacuum pumps but there are electric ones too. they are supposed to be installed with a safety switch. I do not feel an electric is a good way to go. one possible scenario could be a fuel line brake between carb and pump.....with a vacuum the engine dies and the pump loosing vacuum dies too. the electric in the same case can continue to flood a hot motor with gas until you turn off the key while some peoples first instinct is to hit the starter.

my original fuel pump on the 150 was not delivering enough fuel at wide open throttle so i put an after market vacuum pump on and have not had any further problems. john