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nattybumppo
12-22-2013, 09:31 PM
I have heard that if you put an electric fuel pump in-line between the tank and the mechanical fuel pump, it works pretty well. Eliminates vapor lock, and the mechanical pump regulates the pressure to the carb. Has anybody tried this? I am having some starting issues and am curious if this might be an improvement that would also fix that.

SteveH
12-23-2013, 06:49 AM
I have done this, and it has saved my bacon many times on hot days. I used a 'Mr. Gasket 105 pump' (search eBay with those terms).

To solve various fuel pressure problems, I had replaced the OEM pump 2x and rebuilt it once, but cannot seem to hold good pressure on very hot days. I also have tried many other pumps through the years, including the classic Carter electric pump, and the short-lived Holley motor driven pumps (junk, IMO). Do not use the $29 'vibrator' type pumps - they don't put out enough pressure. I mounted my pump very low in the system - below the battery tray. This makes the pump gravity fed with fuel from the tank. I also have a regulator and small gauge on the output. I run the regulator fairly high - something like 7 psi, which is the max pump output. But, I notice that on hot days, the output can drop to 3 psi. I tried running the electric pump at 3-4 psi, but that wasn't enough.

Beware that anytime you run an elec. pump in front of a mechanical pump, you risk a rupture (someday) in the mech. pump diaphragm and flooding the crankcase with gas. To prevent this, you can entirely remove the mechanical pump and replumb the system.

The Mr. Gasket pump is fairly noisy, and I have it powered through a relay and switch, so I can turn it off for testing or safety reasons. It only runs in the 'ign' position, not accessory.

With the junk summer gasoline we now get, this has been the only pump that has reliably solved my vapor locking issues. Note that my carb fan is working, my carb is freshly rebuilt, my fuel filter is clean, etc. Still, after a 15 minute park on a hot day, I can suffer from hot soak problems and the truck will sputter to life with a big black cloud blowing out the tailpipe. The electric pump did improve cold starting, as you can run the pump for a couple seconds to fill the carb before you start cranking.

YMMV - but this is what works for me.

subzali
12-23-2013, 08:22 AM
Sascha, have you had this issue for a while or has it been recent? Is it affected by temperature?

My '77 with no carb cooling fan and OEM fuel pump has been fine, hot or cold, high and low. Sometimes it'll get a little heat soak going and take slightly longer to start up, but it always does. I do have a fully electronic ignition from a '79, don't know if that makes a difference. Also OEM plug wires.

I'd like to know more about your symptoms. Is it cold starts or hot starts that are causing you problems?

nattybumppo
12-23-2013, 04:39 PM
Long-term symptom: vapor lock at high altitude (top of Argentine Pass when I turned it off).
Short term symptom: hard starting when warm. It fires right up first thing in the morning when I double pump and choke it, but when it sits for a while, it takes several long turns of the key until it finally fires up...and then it blows "black smoke" according to Steve. This happened after the last meeting (really cold out) but also recently when it has not been that cold out. Seems like it isn't getting fuel...but it could be spark I suppose. Engine rebuilt 6K ago, but I did not replace the fuel pump. Plugs were new at that time, and fuel filter replaced. Carb rebuilt less than 1 K ago with Ricardo's help, and it has been running great until it started to get colder out. There seems to be plenty of fuel in the bowl when I have checked it, but I have not looked at that during the hard-starting episodes (usually at night and cold out.

Crash
12-23-2013, 05:12 PM
It WAS cold after the meeting and Ripper was acting as if he was flooded while you were starting him. With the rebuilds you've done recently, you might think it's something like the fuel pump causing problems, but I don't know. Could it be something procedural? Over pumping the throttle after the truck has set for awhile but hasn't gotten fully cold? Certainly don't want to be washing the cylinder walls with a too rich mixture if not necessary. Float set just right?

nattybumppo
12-23-2013, 07:53 PM
Yeah, but it has been a no-go when I try to start it with no gas at all too. Though after several attempts with no gas and the starter turning and turning, I do eventually resort to pumping the pedal. Still, I am sure there is something going on in there besides me being a dummy (which is, of course, beyond dispute!).

Air Randy
12-24-2013, 08:55 AM
Do you have an automatic choke or manual choke? If auto, how is it adjusted?

kurtnkegger
12-24-2013, 02:55 PM
I had a similar problem that turned out to be my coil failing. You may be on to something when you stated it may be a spark issue. My problem was pretty random, but seemed worse when warmed up.

nattybumppo
12-24-2013, 09:25 PM
I had a similar problem that turned out to be my coil failing. You may be on to something when you stated it may be a spark issue. My problem was pretty random, but seemed worse when warmed up.

Interesting. Hadn't thought of the coil...thanks, Kurt

nattybumppo
12-24-2013, 09:25 PM
Do you have an automatic choke or manual choke? If auto, how is it adjusted?

Manual choke...a primitive beast it is.

subzali
12-24-2013, 09:36 PM
I am inclined to think it is some electrical issue as well, that's why I qualified my post by stating what ignition I have and that I have OEM plugs.

Have you checked your spark plugs for indications of poor/weak spark?

An easy way to test your fuel pump would be to get a pressure gauge and tee it into the rubber discharge of your fuel pump. I think it should be 3-4 psi; I would have to look in the FSM to be sure. Having good pressure helps prevent fuel from vaporizing, so an electric fuel pump could help there. On the other hand, it may be masking other symptoms.

Rzeppa
12-31-2013, 08:04 PM
My red top blem in my 71 is almost 13 years since I put it into service and is starting to get soft, thus I have been having starting issues this winter. Since I have the "non-USA" distributor I also utilize the non-OEM ballast resistor in series with the coil positive lead. What I have been doing lately is jumping directly from the battery + post to the downstream side of the ballast resistor and she starts right up.

But I have also had the heat soak and stuff at high altitudes even with known good OEM pumps. Both on my 40s and my 60.

To speak to the original question, it is probably not harmful to put a mild electric pump upstream from the mechanical pump, just make sure that it isn't made for MPI, which uses a much higher pressure than TBI. My daughter's 60 had an electric in it when she bought it, it crapped out pretty quick. She got some Autozone generic replacement and it would put out so much pressure that it would stick her bowl needle and cause starvation. When we ditched it and put in an OEM mechanical everything started working like the factory intended.

Crash
12-31-2013, 09:46 PM
<snip>
When we ditched it and put in an OEM mechanical everything started working like the factory intended.

Amen.
Happy New Year.