Can I bypass the mechanical pump?

[steve91tt]

I am still troubleshooting my fuel system. History in the following post...

http://www.classiczcars.com/forums/showthread.php?t=37722

I have a clean tank, new filters and I blew down the fuel lines. The car runs great 95% of the time but now and again it tries to die when idling. I pulled the return line (after the restriction orifice) and ran it into a gas can. I get lots of fuel flow from the return line but it spits and pops like I would expect it to look if the gas was boiling in the line.

I'm running out of things to test but I thought I would try to take the mechanical pump out of the equation in case a blockage in the pump is causing an intermittent problem.

Is it possible to bypass the mechanical pump and run the car on the electric pump alone? I assume the car will run fine but I don't have a block off plate so I can't take it off the car and I am worried about burning up the mechanical pump with no gas running through it to provide cooling. Anyone ever tried this?

[d240zx2]

I've had nothing but an electric pump for years. Fab a block-off plate from 1/8 to 1/4" plate, it's pretty easy to do. Use a gasket as your form and to seal the opening.

My pump is a Stewart-Warner "clicker" pump putting out about 5 psi feeding triple Mikunis. Mounted externally of the gas tank, it feeds through a 3/8" line to a fuel distribution block, then to the individual carbs. An inline fuel filter in conjunction with the filter in the pump keeps gas clean to the carbs.

[jmortensen]

Literally bypassing the mechanical pump is a bad idea. I ran a hose from the inlet to the outlet when I first ran the electrical pump, because I wasn't sure it was going to work as I wanted, so I wanted to be able to plug the mechanical pump back in if necessary. The mechanical pump is cooled by the fuel that flows through it. If you cycle the same fluid through it gets too hot and the diaphragm bursts and you get a engine compartment anti-rust treatment in the form of oil spraying all over the place.

If you want to get rid of the pump, get or make a block off plate.

[Bonzi Lon]

What about taking off the fuel pump cam for a short amount time for the test? Route hoses around the mechanical pump.

Bonzi Lon

[steve91tt]

Literally bypassing the mechanical pump is a bad idea. I ran a hose from the inlet to the outlet when I first ran the electrical pump, because I wasn't sure it was going to work as I wanted, so I wanted to be able to plug the mechanical pump back in if necessary. The mechanical pump is cooled by the fuel that flows through it. If you cycle the same fluid through it gets too hot and the diaphragm bursts and you get a engine compartment anti-rust treatment in the form of oil spraying all over the place.

If you want to get rid of the pump, get or make a block off plate.

That's what I was afraid of.

I think I will just order the block off plate and deal with it next weekend.

Thanks for the feedback everyone.:classic:

[olzed]

I have been running an electric pump on my 240 for 10 years. I removed the pump arm that connects the cam,and routed the fuel through the mechanical pump so it looks origional. Not even show judges have spotted the change.

From memory I cut a full gasket to stop any leakage of gas or oil.

[jmortensen]

I have been running an electric pump on my 240 for 10 years. I removed the pump arm that connects the cam,and routed the fuel through the mechanical pump so it looks origional. Not even show judges have spotted the change.

From memory I cut a full gasket to stop any leakage of gas or oil.

That's the way to do it if you want to leave the pump there, but really making a block off plate is pretty simple.

If you're deleting things, you can also get rid of the stock fuel rail if you want. I did that because I was having vapor lock trouble at the track, and I found that the rail and the pump were both too hot to touch after the car had been running for a while. After removing both and running a rubber hose from the filter across the rad core support and back to the carbs, I never had vapor lock again.

[steve91tt]

That's the way to do it if you want to leave the pump there, but really making a block off plate is pretty simple.

If you're deleting things, you can also get rid of the stock fuel rail if you want. I did that because I was having vapor lock trouble at the track, and I found that the rail and the pump were both too hot to touch after the car had been running for a while. After removing both and running a rubber hose from the filter across the rad core support and back to the carbs, I never had vapor lock again.

Great tip! Thanks.