1940 PT105 - Electric Fuel Pump

[Splitpi]

I have a 1940 Plymouth PT105.   Same period motor (from a 52', P23 code 218ci ) and has the floor starter, 6V Positive Ground, BB1 Carb, etc...  Lately, the truck is not running due to a host of fuel related issues and my slowness on working on it between work, family, and the Texas heat.  I have replaced the fuel tank (which I had sealed about 7 years ago, but has come undone) due to corrosion with a "Tanks Inc 39DP-T" from Summit Racing.  The new tank fits great, and I am now in the process of running all new fuel lines from the tank to the mechanical pump (which I replaced, but I don't have faith in it, could not prime, or was pushing too much pressure when primed, etc..). 

 

I am looking at switching to an electric fuel pump as part of adding in the new fuel lines.     Using 5/16" Copper Nickel hard lines with double flair fittings for the fuel line.   I'll also do another carb rebuild to make sure it is clean and put this filter pre-pump.  Had a paper/plastic one between the mechanical pump and carb prior.    I think the electric pump gives me better assurance that the fuel system is working up to the carb.  This would completely remove the mechanical pump and I would put a block off plate on the motor.

 

Parts: 

• Carter P4259 Fuel Pump
• 20 Amp slow burn fuse & holder
• 6V Relay
• OS75 Oil Switch
• K&N 81-0300 Fuel Filter
• 5/16" Hardline and various fittings
• Inertia Switch

 

Thoughts?  Does this wiring look correct?

Edited January 28, 2022 by Splitpi

[Splitpi]

Also, Attached is another version with a priming switch incase the truck has sat for a long period and the carb is dry.   Is this overkill?

[JBNeal]

I have heard of a setup where the mechanical fuel pump is retained and the electric fuel pump is only used to prime the system, so the priming switch makes sense with that configuration.  An ignition keyswitch with the starter crank position beyond ignition could be used to prime the fuel pump without adding another external switch.  I do not know what the threshold is for the pressure switch to be active, so it may be possible that 2-3 seconds of cranking may build enough pressure to activate the switch.  And therein lies the issue with these circuits:  the functional attributes of that pressure switch.  If you have the switch, it might help to rig up a test with a voltmeter to monitor when the switch activates while cranking.

[Jeff Balazs]

I have a full time 6v Fuel pump on my 52 B-3-C and it works great. One thing that is very important is to a good pre filter ahead of the fuel pump. When I built my system I came across info that indicated that the main cause of pump failure was dirt getting into the pump. Mine has been in daily service for over 7 years with no problems. I also have a pressure regulator ahead of the carb and another canister type filter there too. Like I said no problems at all with the fuel system this way.

Hth, Jeff

[Splitpi]

I was talking it over with a friend, I think the oil pressure switch may be a bit of an overkill and I plan to not use it.   Inertia Switch is simply a safety thing.   

I do have a fuel pressure regulator that I can put in near the Carb, but I would like to not use it if possible.  The need for several fuel filters does make sense and I was planning on one pre-pump.  I have ordered the parts, so I'll set it up and see if the circuit works as intended.  

 

Another thing I read else where was to put a return line off of the carb and back into the tank.  Basically install a T near the carb and put a fitting for the return that is brazed shut.   Then drill a small hole like 1/16th through the brazing as a flow restrictor.   Basically to release pressure on the carb input needle valve.  

Edited February 2, 2022 by Splitpi

[Jeff Balazs]

IMO the return line is not needed. Good filtration and the use of additives has worked well for me. 4oz of MMO every other tank gets the job done.

Hth, Jeff

[Los_Control]

8 hours ago, Splitpi said:

Another thing I read else where was to put a return line off of the carb and back into the tank.  Basically install a T near the carb and put a fitting for the return that is brazed shut.   Then drill a small hole like 1/16th through the brazing as a flow restrictor.   Basically to release pressure on the carb input needle valve.  

While I do understand many have installed a electric pump in the system just to prime the engine before starting ... seems it would be a handy feature to have available.

After prime they shut it off and run off the mechanical pump.

 

I dunno, I bought a mechanical fuel pump from Napa a couple years ago. If truck sits for a few months, it takes a bit of cranking to prime ... but it always does. So far.

I wonder if too much fuel pressure is not actually crap from your old tank disintegrating & causing the floats in the carb to stick?

Would a new tank, fuel pump, carburetor tear down and clean correct your current problems?

 

The return line you speak of sounds like a good idea. I think Uncle Tony explains it really good here.

 

[NiftyFifty]

I would actually say that pump puts out too much pressure for a single carb, you only need a 2-4lb pump or you definitely need to install a fuel pressure regulator.

 

I ran an electric from day one in my truck, and yes lots of good help above, in regards to a good pre filter and also make sure the pump is as close to the tank as possible, as the like to push, not pull.

 

I did run just a straight key on with a fuse, so it did run constantly in the on position, but I was 12 volt and had a ignition with an accessory setting to run anything I desired without the pump going, but your ideas are a safer way to go.  

[bkahler]

Here's where I mounted the electric pusher pump.  It's a Carter P4070 pump. (Should have mentioned, it's a 12 volt pump)

 

Edited February 3, 2022 by bkahler

[Bryan]

I went and bought an Airtex E8902  since the Carter pump looked like it had too high pressure and flow.  Somewhere I posted about it.

[1949 Wraith]

I run, on all my vintage vehicles, Airtex style fuel pumps as a fuel primer if needed with the normal mechanical pump while driving. 

 

The Airtex are a pulse style and allow fuel to drawn through them when not engaged. The Carters pumps do not allow fuel to be drawn through them when not engaged, so they will not work as a primer pump for a mechanical pump use.

 

If I was to do a mechanical fuel pump delete I would chose the Carter style as they look more robust. There is an issue that I have heard of though, where Carters can overheat in low fuel requirements like a parade, as the gas flow acts as a coolant.

[Splitpi]

All,

 

Thank you for the follow up.   I was torn between the Airtex E8902 and the Carter E84259.   I have read also that the Carter info may be inaccurate and over stated.   

[NiftyFifty]

To be honest, the shop I used to work at quit using all carter pumps…nothing but trouble.  Airtex seem to be on for the price point 

[bkahler]

My experience with Carter pumps have been just the opposite.  They are the only ones I've found to stay running.

[maok]

I've been using a cheap Chinese pump ($15) for at least 3 years now, have one in both my mopars, one in the trunk as a spare as a just incase, an expensive Facet pump failed after 12 months.

 

Two things you need with any electric fuel pump, a good fuel filter before it, and not let it run dry ie run out of fuel.

 

And mount it at the bottom level of the tank and near it.

[chrysler1941]

?

Edited February 5, 2022 by chrysler1941

[Bryan]

Haven't used it yet, just recently bought. I think Airtex and Carter are made by the same company, or have the same parent.

[1949 Wraith]

2 hours ago, Bryan said:

Haven't used it yet, just recently bought. I think Airtex and Carter are made by the same company, or have the same parent.

Thats what I heard that Carter had bought out Airtex. For a while there it was hard to find a low pressure 6 volt Airtex not sure if it has improved.

[bkahler]

On 2/3/2022 at 8:48 AM, 1949 Wraith said:

....The Carters pumps do not allow fuel to be drawn through them when not engaged, so they will not work as a primer pump for a mechanical pump use.

 

 

This is not true.  I know of many motorhome owners who have the Carter P4070 pump on their motorhomes and they only turn the pump on when they approach a grade or when first starting the vehicle.  Normally they just rely on the mechanical pump for operation.  I don't run my pump that way but it does indicate that you can pull fuel through the Carter pump when it is turned off.

 

[Splitpi]

Great information provided here.   Greatly appreciate it.  

I am now torn on whether to use the Airtex as booster (always on) to the mechanical.   Or the Carter / Airtex as stand alone without the mechanical.    I am still thinking I should still run a pressure regulator (have a Holley 12-804), though a return line at the carb would definitely allow for better control of over pressure than just a mechanical regulator alone.... or a regulator with the return line (though I cannot find one with a return line and less than 4 psi).  

[bkahler]

34 minutes ago, Splitpi said:

Great information provided here.   Greatly appreciate it.  

I am now torn on whether to use the Airtex as booster (always on) to the mechanical.   Or the Carter / Airtex as stand alone without the mechanical.    I am still thinking I should still run a pressure regulator (have a Holley 12-804), though a return line at the carb would definitely allow for better control of over pressure than just a mechanical regulator alone.... or a regulator with the return line (though I cannot find one with a return line and less than 4 psi).  

 

I'm curious as to how you would implement a return line?  My assumption is a return line needs to be directly fed into the tank which means you would have to add another port to the tank.  Is there another way to run a return line?

 

 

 

[bkahler]

I should add I think the return line concept is an interesting one.  I have a 1994 Cushman Truckster that has a little 22 hp motor using a Walbro carburetor.  It came with an electric pump and a return line setup from the factory.  The fuel filter itself had the return line port which makes for a very simple arrangement.  

 

[1949 Wraith]

1 hour ago, bkahler said:

 

This is not true.  I know of many motorhome owners who have the Carter P4070 pump on their motorhomes and they only turn the pump on when they approach a grade or when first starting the vehicle.  Normally they just rely on the mechanical pump for operation.  I don't run my pump that way but it does indicate that you can pull fuel through the Carter pump when it is turned off.

 

I stand corrected, but it might have something to do with a high pressure mechanical pump on the motorhome as opposed to our 3-4 psi pumps? 

[Jeff Balazs]

Fwiw I would not concern myself with a return line. It just isn't required. A couple of other things that should be considered are deleting the mechanical pump....which is a potential source for fuel in the crankcase. And the use of sealed canister type fuel filters which reduce the chance of leaks. A pressure regulator makes a lot of sense. Keep it all simple and easy to maintain. You will be happier in the long run.

Jeff

[bkahler]

19 minutes ago, 1949 Wraith said:

I stand corrected, but it might have something to do with a high pressure mechanical pump on the motorhome as opposed to our 3-4 psi pumps? 

 

If I remember right the stock GM mechanical pump puts out around 6 psi.  The surprising thing is on a 31 foot motorhome it's pulling from the tank which is about 20 feet away.  That's a long stretch for a mechanical pump to suck fuel from the tank, through an electric pump no less when the pump is off.  The real reason for the addition of the electric pusher pump is for grades.  The engine requires so much fuel the mechanical just can't keep up.