Fuel pump?

[Eagle]

Humor me.

 

I'm a certified Olde Pharte -- I grew up in the age of carburetors, and I know and understand carburetors. Sure, EFI has advantages, but the single injector on the Renix 2.5L throttle body injections systems is expensive. There are advantages (in my mind, at least) to eliminating the TBI and installing a carburetor.

 

The "gotcha" is that the factory fuel pump puts out too much pressure for a carburetor. Carbs need about 7 psi. I have a brand new in-the-box Stewart-Warner fuel pump, left over from the days when mechanical fuel pumps for Hudsons became unobtanium so we had to convert them to electric. The question is how to make that work with a Comanche gas tank.

 

Would it be possible to gut a factory fuel pump and then reinstall it to act as nothing more than a fuel pickup?

 

Any other suggestions?

[Pete M]

have you seen that there's a GM injector that works? 

[eaglescout526]

Try this theory I have. I would set up a EFI fuel pump, put some hoses on it and put the pump you want in the series and see if that pump will pull fuel through the old pump. I don’t see why it wouldn’t cause the fuel should still come through the pump regardless. 

[jdog]

two options:

1: pressure regulator

2: remove in tank pump, add line to get to same length as pump and install screen, install pump on frame

[Ωhm]

1 hour ago, Eagle said:

The "gotcha" is that the factory fuel pump puts out too much pressure for a carburetor.

and require a fuel return line.

 

1 hour ago, Eagle said:

Carbs need about 7 psi.

Do carbs require a fuel return line?

[Eagle]

8 hours ago, Ωhm said:

 

Do carbs require a fuel return line?

 

Nope -- not with the fuel pumps we had. A carburetor works by having the fuel pump push gasoline into a reservoir in the carburetor called a "float bowl." Inside that there's a float, not unlike the float in the gas tank for the gas gauge, but smaller. The float is connected to a small, polymer-tipped needle that points into the orifice of the fuel inlet. When there's enough gas in the bowl, the float presses the needle into the seat (the orifice) hard enough to shut off the flow of gas against 7 psi of pressure. As gas gets suck out and burned, the float drops, releasing the needle valve and allowing more gas to flow.

 

That's not to say that a carb couldn't be rigged with some kind of fuel pressure regulator that would return anything over 7 psi to the tank. I don't know if such regulators exist, but it's entirely possible.

[jdog]

12 minutes ago, Eagle said:

 

Nope -- not with the fuel pumps we had. A carburetor works by having the fuel pump push gasoline into a reservoir in the carburetor called a "float bowl." Inside that there's a float, not unlike the float in the gas tank for the gas gauge, but smaller. The float is connected to a small, polymer-tipped needle that points into the orifice of the fuel inlet. When there's enough gas in the bowl, the float presses the needle into the seat (the orifice) hard enough to shut off the flow of gas against 7 psi of pressure. As gas gets suck out and burned, the float drops, releasing the needle valve and allowing more gas to flow.

 

That's not to say that a carb couldn't be rigged with some kind of fuel pressure regulator that would return anything over 7 psi to the tank. I don't know if such regulators exist, but it's entirely possible.

Like a Tolet fill valve,  or a swamp cooler.

Yeah there are regulators with return lines

[derf]

It's always a good idea to have a pressure regulator with a bypass return line when you run an electric pump.  The constant flow of fuel keeps the pump cool.  It's not mandatory, just a good idea.

 

You can fit a length of hose in place of the pump and install an external pump.

 

Depending on the pressure provided to the TBI, you maybe could just put in a pressure regulator with the factory pump.  If it's like GM TBI with 15 PSI it could work.  If it's up above 40, a pressure regulator may not work.

 

But I'd personally try to get the TBI running.  I like it over a carburetor any day.

[89 MJ]

I know that you have an electric fuel pump on hand, but if you truly want old school, is there any way you could run a mechanical pump? Personally, I prefer a manual fuel pump with carbs anyways. 

[Ωhm]

17 hours ago, Eagle said:

When there's enough gas in the bowl, the float presses the needle into the seat (the orifice) hard enough to shut off the flow of gas against 7 psi of pressure. As gas gets suck out and burned, the float drops, releasing the needle valve and allowing more gas to flow.

 

A pump can be deadheaded for short periods of time, especially if pump has build in slippage (re-circulates).

[Eagle]

On 3/14/2021 at 8:47 AM, 89 MJ said:

I know that you have an electric fuel pump on hand, but if you truly want old school, is there any way you could run a mechanical pump? Personally, I prefer a manual fuel pump with carbs anyways. 

 

Nope. The 2.5L blocks didn't have any provision for a fuel pump after 1985. In any event, those old fuel pumps were notorious for having the internal diaphragm rupture, which tended to fill the crankcase with gasoline and then stranding the vehicle.