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Old 09-09-2018, 03:46 PM   #1
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Question Bypass electric pump

OK barners I installed an inline electec fuel pump on my 55 with 272 engine and now if I drive it 55 or 60 it will starve for fuel after a few minutes..Hold the pump in the on and ok for a bit..So I need a plan that will allow the mechanical pump to suck gas around the electric pump..Do I need a check valve in the bypass line so the electic pump can not push the fuel back through the bypass line rather than up to the carb..Someone out there must have a plan and give me an idea as to how to go about it..I only use the electric for starting when the car is not driven fo long periods Thanks in advance..PS Mechanical pump is new..
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Old 09-09-2018, 04:44 PM   #2
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Default Re: Bypass electric pump

I'm curious as to what kind of pump you have that will pull some through, but not enough. I would first be sure that you do not have a connection after the electric pump letting the mechanical pull air. If all that is good, yes you will need a check valve in the loop. All those extra fittings are places that can leak fuel or air.
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Old 09-09-2018, 05:15 PM   #3
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Default Re: Bypass electric pump

The electric comes from Macs and I believe it is a carter..That said NO there is no other fittings in the line but the electric pump..I have a Skips check valve that I tried but it seemed to be stuck a lot of the times which I blamed on ethanol in fuel Could maybe use that in bypass or a filter with a check valve in it..???
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Old 09-09-2018, 07:57 PM   #4
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Post Re: Bypass electric pump

To do what you want to do (prime only) and if the electric pump is not rated flow-thru, it needs to be on a bypass circuit with one way flow valve as shown-


And don't forget to test fuel pressure after work - both/either pump).



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Old 09-09-2018, 09:59 PM   #5
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Default Re: Bypass electric pump

I noticed lately that one of the resto parts suppliers is offering a 6-volt electric fuel pump, so I thought about adding it to my '55 just for priming the carburetor. My guess is that the electric pump would need to be installed downstream of a "tee" fitting off the main fuel line (maybe somewhere near the steering gearbox). then pipe up to the tubing between the mechanical pump and carb with another "tee". But then there would need to be a check valve to prevent fuel from the electric pump backfeeding the line to the mechanical pump and probably need to have another check valve from preventing normal fuel from the mechanical pump backfeeding the line from the electric pump. Not sure what these alleged check valves would be (for 5/16" tubing). Never seen one.
The photo that KULTULZ shows is apparently a different arrangement whereby the the electric pump feeds into the mechanical pump (but only requires one check valve to prevent fuel from backfeeding into the tank instead of to the carb.) Not sure if it is a good idea to force fuel through the mechanical pump prior to the engine being cranked.
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Old 09-09-2018, 10:39 PM   #6
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Default Re: Bypass electric pump

There are no issues with forcing fuel through the mechanical pump.
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Old 09-10-2018, 12:34 AM   #7
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Default Re: Bypass electric pump

My electric pushes fuel thru the mechanical and the mechanical will pull fuel thru the electric pump. No check valves or tees. Am I missing something here or am I lucky to have an electric that will let this happen?
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Old 09-10-2018, 04:35 AM   #8
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Post Re: Bypass electric pump

What that check valve in the photo is doing is preventing the electric pump from pressurizing the gas tank outlet line in operation (if used only as a primer). It would push fuel back into the tank while also not fully pressuring the line to the mechanical pump. It separates the mech pump supply from the electric primer pump.

In the "old days" of SUPER STOCK and SATURDAY NIGHT SPECIALS, an electric pump was used @ the tank to deliver fuel to a high capacity mechanical pump where it would control pressure/volume. As time progressed, the mech pump was canned and went to electric with a pressure regulator and return line.

An electric pump is designed to push, not pull, whereas a mechanical can do both. If you use one (electric) as a primer after the mech pump, it also would be subject to blend separation/vapor lock if these occurred before the mech pump or if there was fuel boiling in the fuel line before the electric pump.
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Old 09-10-2018, 05:40 AM   #9
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Default Re: Bypass electric pump

O! Very usefull replies, thx
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Old 09-10-2018, 05:59 AM   #10
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Default Re: Bypass electric pump

Quote:
Originally Posted by 50fordcoupeman View Post
My electric pushes fuel thru the mechanical and the mechanical will pull fuel thru the electric pump. No check valves or tees. Am I missing something here or am I lucky to have an electric that will let this happen?
That is what I expected of mine..Prime to start and forget but after I drive a couple miles it starves for fuel so hold the electric on for aq bit and OK for a bit..OK if I don't drive over 30 mph..
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Old 09-10-2018, 09:20 AM   #11
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Default Re: Bypass electric pump

if you needed a bypass check valve etc. you would have read about the need for one it is not like you are the first to install one.first thing you need to do is bypass the electric pump.pretty simple use a short piece of fuel line.if runs like it used to then.now look at fittings used if they have too small a hole then you are choking the fuel supply thus the need for using electric to boost flow somewhat but never getting full flow.think about it if you made no other changes logic dictates fuel pump or fittings are problem.another thing if you used barb fittings the fuel line can sometimes catch on fitting when sliding on causing a partial blockage.you will not know without removing the thing that led to problem.or bury your head and throw money and time at it good luck
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Old 09-10-2018, 11:00 AM   #12
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Default Re: Bypass electric pump

You need an Airtex E8902 for 6V or Airtex E8016S for 12V.
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Old 09-11-2018, 09:56 AM   #13
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Default Re: Bypass electric pump

My 55 had a 312 with a cam and a four barrel. I had an electric pump for prime, and in a 1/4 mile drag race, the car acted like it was out of fuel. I let off it, counted to three, then opened it up again and all was OK. I have a volume problem. I removed the tank, and Ford left me a flat spot right on top. I cut into it and made a hole big enough to get my hand in. I found two things. The screen was half plugged, and the factory soldered in bulkhead fitting was too small. The fitting took a 5/16 line, but the ID would not pass a 3/16 drill. I plugged the stock bulkhead. I made a new 3/8 line all the way from the pickup to the carb. It never ran out of fuel again.
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Old 09-11-2018, 11:17 AM   #14
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Question Re: Bypass electric pump

Quote:
Originally Posted by Daves55Sedan View Post

Not sure if it is a good idea to force fuel through the mechanical pump prior to the engine being cranked.
Why not? The worst that can happen is a fuel pressure/volume restriction (the old days I mentioned above was pumped through a high pressure/high volume mech pump - CARTER). Or worst case scenario if the mech pump fails, it electric) will fill the crankcase with fuel.

Again, an electric pump is designed to push fuel. If one uses it to pull full, the fuel system is subject to blend separation/vapor lock, the same thing you are trying to avoid.

Don's description was for a race car. The first thing you do there is to increase fuel line size for volume. If you need that on a driver, you have other problems.
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Old 09-11-2018, 06:46 PM   #15
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Default Re: Bypass electric pump

Quote:
Originally Posted by estout81 View Post
You need an Airtex E8902 for 6V or Airtex E8016S for 12V.
Correct
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Old 09-12-2018, 08:43 AM   #16
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Default Re: Bypass electric pump

what I think Don was saying the fitting was to small(meaning the ID ) nothing to do with a race car.he happens to race his car at times.what he said and I agree on the fitting as I advised both of us are speaking from experience not hypothetical.no need to add all that junk as I said never read anywhere about anyone having to use a bypass check valve.
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Old 09-12-2018, 09:18 AM   #17
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Question Re: Bypass electric pump

Quote:
Originally Posted by 54vicky View Post

...what I think Don was saying the fitting was to small(meaning the ID ) nothing to do with a race car.he happens to race his car at times.what he said and I agree on the fitting as I advised both of us are speaking from experience not hypothetical.no need to add all that junk as I said never read anywhere about anyone having to use a bypass check valve.
What I understood from Don's post is that the OEM style fitting (@ fuel tank bung) was restrictive. When the car was operated as a PASS CAR with mech pump, the restriction did not manifest itself.

Only when he used a in-line primer pump and raced, the volume could not keep up with demand.

I also like to think of my speaking from experience.

The OP wanted opinions on how to add a primer pump with a by-pass. Do you know of a cheap primer pump that is flow-thru rated?
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Old 09-12-2018, 09:55 AM   #18
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Default Re: Bypass electric pump

The first electric FP I used was the little rectangular cheapy. The stock pump on the motor pulled through it just fine. It worked great for priming. When I went to the 3/8 line, I upgraded the electric to a Holley race style from Jeggs. The pump on the motor had been a stock type replacement. It fit passenger cars with an adapted fitting, 292 trucks, and FE motors all the way up to 427. I never saw a problem with any of the pumps pulling or pushing through another. My electrics were mounted under the back seat on the outside, near the tank. I also had a heat shield between the pump and the exhaust. I used the Jeggs wire kit with a relay. Good parts, good folks to deal with. The volume problem at the drags was because of a darn nice burn out, then a hard pass, ( is there any other kind?). The new 3/8 line fed the stout Y block at Bonneville in a one mile pass.
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Old 09-12-2018, 11:16 AM   #19
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Default Re: Bypass electric pump

Just adding this to the mix...
I ordered a replacement for the flexible fuel line that connects from the steel line near the steering box over to the fuel pump.
The replacement had a noticeably smaller inside diameter than the one I took off so I returned it and made my own with more normal sized fittings.

Also, I've heard these flex hoses can swell up inside from ethanol in the gasoline, restricting the fuel flow even more.

photo: old take-off on the left, new replacement on the right
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Last edited by dmsfrr; 09-12-2018 at 11:44 AM.
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Old 09-12-2018, 04:09 PM   #20
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Default Re: Bypass electric pump

if a big if he gets back with the ID size of fittings and if he bypassed ep then we may have the answer
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