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Electric fuel pump push fuel through a mechanical pump
Posted By: RUNCHARGER
Electric fuel pump push fuel through a mechanical pump - 03/03/15 03:08 AM
Enough's enough with this crappy fuel we have today. I am not running my cars for one more season having to prime the carbs by hand anymore.
School me on electic pumps, I would like to install an electric fuel pump in both cars just to prime the darn carbs after sitting. I would just as soon keep the mechanical pumps for when the cars are actually running as I don't need the electric pump noise.
Will the electric pump push fuel through the mechanical pump when the engine is not running?
The way I see it I can mount the electric pump parrallel to the regular fuel line near the tank where it's supposed to be or in parrallel to the mechanical pump but that's not where an electric pump is supposed to be. I plan on going parralel either at the back or the front with a check valve in the other line to prevent it pumping backwards back to the tank.
Sheldon
Posted By: RapidRobert
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 03:24 AM
Quote:
Will the electric pump push fuel through the mechanical pump when the engine is not running?
No cuz one valve has to be closed when the other is open, tho an elec pump would likely pressurize the mech pump sufficiently so you wouldn't need to hand prime anymore. (& a mech pump will pull fuel thru the elec pump even if the elec pump ain't running) so you might be able to use the elec to help prime it tho I ain't sure if the elec would up the psi at the carb enough to need a reg. Consider this a BTT & wait for experienced others to chime in
Posted By: calrobb2000
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 06:49 AM
hi
yes a elect pump wll push fuel through a mech pump .
i have had mine that way for years .
drain holley change jets hit switch ad refill carb before starting engine .
1 problem in hot weather mech pump will sometimes not pull enough fuel through elec pump for climing steep grades or w o t operation in which case i flip the on switch and prob solved .
Posted By: RapidRobert
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 06:56 AM
Quote:
yes a elect pump wll push fuel through a mech pump.
Ahhh I learned something today 
Posted By: StealthWedge67
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 06:56 AM
Something is wrong if you're having to prime the carb everytime you start your car. The carb should have gas in the fuel bowl without needing the pump to fill it each time. I can let my car sit for a month or more, and it fires right up with no choke, my setup is just a Carter street pump feeding a Holley double pumper. The question you should be asking is why is my carburetor empty and where is the fuel thats supposed to be in it going?
My 2-cents says you've got other problems. I wouldn't be suprised if you're dealing with a flooding issue, not lack of fuel (??).
Posted By: SSAAHemiFan
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 07:35 AM
I've run the holley red as a push thu to a carter mechanical pump for years.
Depending on you quality of fuel you will have evaporation problems. Ethanol is mandatory around here - Everyone told me it was my carb - I switched over to pure gas - ( Stromberg carb so it isn't something easy to just jet up) and all the problems went away.
I have used one of those cheap square Facet pumps just to prime or to help prevent vapor lock on very hot days and it worked fine.
Edelbrock has there own version. I was going to try one of those in the future.
Posted By: Jack Zupan
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 03:22 PM
I've had this problem with my Roadrunner when it had a 383 and now with a hemi. I would have to crank the engine for a very long time before it would start. I put a small electric fuel pump next to the tank and use it only to prime the carbs. It works like a charm. I then outsmarted myself, I added a vapor separator and 1/4" return line to look like a hemi setup. The electric pump only had enough pressure to run the fuel back to the tank through the return line. Pinched off the return line and now it works fine again. Don't forget you need a low pressure electic pump or you will blow out the carb seals.
Posted By: mikemee1331
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 04:04 PM
a nice Carter 4070 series pump would be the ticket for this. 6psi with plenty of flow. the down side is if there is an issue with the diaphragm in the mechanical pump you flood your oil with fuel without knowing it....
Posted By: DaveRS23
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 04:32 PM
It will work fine but you do not have to run parallel lines. I have a Holley electric back by the tank and it pushes through the mechanical just fine. I have both a manual switch under the dash for priming and the like and a micro switch that is actuated by the secondaries on the carb.
That way, I don't have to listen to the electric pump all the time, but have the flow when I need it. This system has fed the Dominator on the street and track for years now.
Posted By: gdonovan
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 06:00 PM
Quote:
It will work fine but you do not have to run parallel lines.
Nope.
I have done this for over 20 years. I started off with just an electric pump but even the best ($$$) seemed to burn up with all the driving I did.
Under the hood I have a Carter race mechanical pump and out back I have a Carter electric pump mounted in the trunk with a large Fram race filter.
When I start the car I kick on the electric pump till I hear the bowls fill and pressure stabilize. Pump 4-5 times and hit the key and it lights right off. Shut down the electric.
For most of your futzing around driving the big mech under the hood will provide enough fuel. Sustained WOT just hit the dash switch to turn the pump out back on and hammer away. Been meaning to add a WOT switch or even a low fuel pressure switch to have it kick in automatically but its been that way for so long its second nature now.
The gas around here is junk and evaporates in nothing flat. Even with the Carters on top of the tunnel ram out in the breeze the fuel is gone in a day or two.
Posted By: astjp2
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 06:07 PM
I looked at doing this and using a 5 second relay: ignition on, 5 seconds of priming, pump off, start engine, ignition off, ignition on, 5 seconds of priming, pump off, start engine...but the relays are 40 dollars each. Tim
Posted By: John_Kunkel
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 09:09 PM
Quote:
Something is wrong if you're having to prime the carb everytime you start your car.
Modern fuel evaporates more quickly depending on its volatility/vapor pressure...it's not at all unusual to have empty bowls after the car sits for an extended time.
Not all electric pumps will allow the mechanical pump to "pull through" when the electrical pump is shut off.
Posted By: Challenger 1
Re: Electric fuel pump push fuel through a mechanical pump - 03/03/15 09:12 PM
I have found using a stock enclosed air filter housing has slowed the evaporation of the fuel in my carb verses a open air, air filter.
Posted By: Jack Zupan
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 01:32 AM
Quote:
I have found using a stock enclosed air filter housing has slowed the evaporation of the fuel in my carb verses a open air, air filter.
What does this mean? Open vs. closed?
Posted By: Wildjones
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 01:51 AM
Quote:
Quote:
I have found using a stock enclosed air filter housing has slowed the evaporation of the fuel in my carb verses a open air, air filter.
What does this mean? Open vs. closed?
I'm thinking he is referring to a snorkel type air filter as being "closed" and a K&N style as being "open".
Posted By: 68jim
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 02:46 AM
I did this exact same thing a few years ago. At some point I even posted all the part numbers for all the fitting and check valve I used for a really compact arrangement. I have mine tucked up in the axle tunnel and it works great. Just switch on for 15-20 seconds and both carbs prime up. Pump gas pedal to set the choke and it fires right up.
Posted By: RUNCHARGER
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 02:55 AM
Thanks for the help guys, there's absolutely nothing wrong with the car just the modern fuel. I have a new small 72GPH Carter but I may buy a 110GPH one instead, I don't want to starve the 528 at WOT. It has the Race Carter mechanical on there with a regulator.
My 472 has a stock Hemi Carter mechanical with of course no regulator. I can prime it without too much trouble through the stock vent tubes but the AVS's under the shaker on the 528 are not so easy and I'll rig it out first and see how happy I am with it.
Sheldon
Posted By: ahy
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 04:57 AM
Electric push through mechanical works for me ('47 Power Wagon). The stock fuel system was prone to vapor lock while running in hotter temps with today's fuel. Hot re-start not possible unless the fuel pump and nearby line was hosed down with cool water. Cold start after sitting required long crank times.
An auxiliary electric pump on a toggle switch mounted to the frame rail near the tank fixed all the above. It is a carb type electric pump set up with a bypass check valve so the engine mounted pump can draw fuel with electric pump off. The check valve is a 3/8" brass version from the hardware store. Other types are available.
Tests include 1) Run down the road in hot weather until she sputters and looses power. Turn electric pump on and smoothes right out 2) Hot re-start. Starts up quickly with electric pump on. Will not re-start with electric pump off. 3) start after sitting weeks or even months. Starts up promptly with electric pump on. Not so with pump off. Lots of cranking.
I kept the original fuel pump because it has integral filter, also since it is original style and because it is reliable in cooler weather.
Posted By: RapidRobert
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 06:52 AM
Quote:
I have a new small 72GPH Carter but I may buy a 110GPH one instead, I don't want to starve the 528 at WOT. It has the Race Carter mechanical on there with a regulator.
I'd run a psi gauge (isolated or otherwise) to the inside & you'd want several psi at WOT in high gear right at the carb inlet fitting(s). On the "otherwise" you wouldn't wanna a direct gauge inside permanently but for a 1 day test you'll know right then if your delivery setup is adequate. You dont wanna fry that beast from it going lean
Posted By: Dr Dave
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 07:55 AM
Please let me know what you come up with. I have a similar setup, 528", dual quads, shaker, not easy to prime the carbs and want to do something with an electric pump.
Posted By: RUNCHARGER
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 09:10 AM
My plan is to loop off at the sending unit, build a bracket that bolts to the tie down attachments (E body) that mounts a 110 GPH electric pump and use the stock 3/8 fuel line up to the HP mechanical pump. All the repro stainless steel fuel lines will be uncut and if I have to run the electric pump all the time that's what I'll do but it sounds like I'll be able to just use it for a cold start and maybe when using WOT in 3rd and 4th. I'll let everyone know after I test it. I'll tie strap a fuel pressure gauge to the cowl when I first install the extra pump.
Sheldon
Posted By: Evil Spirit
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 10:50 AM
If the engine just will not start unless the bowls are hand primed, that's one thing - I would certainly fix that issue.
But I never understand why people want a stone cold engine that has sat even overnight to start instantly in the first couple rotations. Pretty good chance that all the oil has drained back into the pan, possibly draining the oil passages and the oil filter. There is also the possibility of lifters bleeding down. If they have sat overnight, I rarely attempt to fire any performance engine until I've cranked it and seen oil pressure. IMO an engine that needs to crank 10 seconds or so on that first startup after sitting any length of time is actually doing itself a favor and priming the oil system before it starts, and eliminating any possible dry startup damage. Many hydraulic cammed engines will sound totally different on startup if you "pre-lube" them first, since it gives the lifters on open lobes that have bled down a little a chance to pump up fully and "tighten" the valve train up.
Just a little food for thought about starting that engine that has sat for a while - do you REALLY want it to start first roll?
Posted By: Dr Dave
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 06:04 PM
I'm mostly concerned about cam lobe and lifter face wear on cranking without rapid startup.
Posted By: gdonovan
Re: Electric fuel pump push fuel through a mechanical pump - 03/04/15 06:33 PM
Quote:
I'm mostly concerned about cam lobe and lifter face wear on cranking without rapid startup.
My root beer GTX would crank almost 2 minutes with the factory pump before it got fuel to fire off after sitting.
No thanks, I'll take the rapid fire off every time. The 440 in my blue GTX with solid lifter cam was assembled in 92 or 93 and is still kicking ass. Long crank times are not good for a number of components.
Posted By: astjp2
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 12:54 AM
Quote:
If the engine just will not start unless the bowls are hand primed, that's one thing - I would certainly fix that issue.
But I never understand why people want a stone cold engine that has sat even overnight to start instantly in the first couple rotations. Pretty good chance that all the oil has drained back into the pan, possibly draining the oil passages and the oil filter. There is also the possibility of lifters bleeding down. If they have sat overnight, I rarely attempt to fire any performance engine until I've cranked it and seen oil pressure. IMO an engine that needs to crank 10 seconds or so on that first startup after sitting any length of time is actually doing itself a favor and priming the oil system before it starts, and eliminating any possible dry startup damage. Many hydraulic cammed engines will sound totally different on startup if you "pre-lube" them first, since it gives the lifters on open lobes that have bled down a little a chance to pump up fully and "tighten" the valve train up.
Just a little food for thought about starting that engine that has sat for a while - do you REALLY want it to start first roll?
Absolutely, its a lot easier on the starter and the oil pressure comes up faster. Tim
Posted By: RUNCHARGER
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 02:14 AM
Camshaft and lifters are what I am concerned about as well. Solid lifters so they don't bleed down and I don't rev it more than I have to when cold. It cranks for at least 1 minute before firing, that isn't good for anything.
Sheldon
Posted By: ahy
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 02:24 AM
Quote:
My plan is to loop off at the sending unit, build a bracket that bolts to the tie down attachments (E body) that mounts a 110 GPH electric pump and use the stock 3/8 fuel line up to the HP mechanical pump. All the repro stainless steel fuel lines will be uncut and if I have to run the electric pump all the time that's what I'll do but it sounds like I'll be able to just use it for a cold start and maybe when using WOT in 3rd and 4th. I'll let everyone know after I test it. I'll tie strap a fuel pressure gauge to the cowl when I first install the extra pump.
Sheldon
In general the electric pump will not flow fuel when turned off. The mechanical pump will not be able to "suck" through it. An electric pump bypass line with check valve is needed to allow the engine to operate with electric pump off. I used a brass check valve from the hardware store on my truck... more compact automotive type valves are available from Summit and others.
Posted By: DaveRS23
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 02:47 AM
Quote:
Quote:
My plan is to loop off at the sending unit, build a bracket that bolts to the tie down attachments (E body) that mounts a 110 GPH electric pump and use the stock 3/8 fuel line up to the HP mechanical pump. All the repro stainless steel fuel lines will be uncut and if I have to run the electric pump all the time that's what I'll do but it sounds like I'll be able to just use it for a cold start and maybe when using WOT in 3rd and 4th. I'll let everyone know after I test it. I'll tie strap a fuel pressure gauge to the cowl when I first install the extra pump.
Sheldon
In general the electric pump will not flow fuel when turned off. The mechanical pump will not be able to "suck" through it. An electric pump bypass line with check valve is needed to allow the engine to operate with electric pump off. I used a brass check valve from the hardware store on my truck... more compact automotive type valves are available from Summit and others.
Sorry to disagree, but the mech pump WILL pull through an elec pump. I have a Holley pump mounted by the tank that only runs when switched on. 99% of time the mech pump runs the Cuda pulling fuel through the elec pump. Been that way for years now. And this is the second or third car I have plumbed like that.
Just sayin'.
Posted By: gdonovan
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 02:53 AM
Quote:
In general the electric pump will not flow fuel when turned off. The mechanical pump will not be able to "suck" through it.
I have been doing it for 20+ years.
Others have chimed in not just the Carter pumps allow this too.
Posted By: HEMIDOG 70
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 03:36 AM
Quote:
Please let me know what you come up with. I have a similar setup, 528", dual quads, shaker, not easy to prime the carbs and want to do something with an electric pump.
X2 no shaker here but I too would like to add a electric pump to prime for starts due to evaporation. I'm running a 528 hemi with dual quads and solid lift cam. I have extended crank times after the car has sat for longer periods.
Posted By: Dr Dave
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 08:33 AM
Ok, looks like whoever puts this together best is in business! Let us know what you did, what you used, heck, I will buy your "kit"!
Posted By: Jack Zupan
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 03:55 PM
Sorry to disagree, but the mech pump WILL pull through an elec pump. I have a Holley pump mounted by the tank that only runs when switched on. 99% of time the mech pump runs the Cuda pulling fuel through the elec pump. Been that way for years now. And this is the second or third car I have plumbed like that.
Just sayin'.
Same here, Carter pump plumbed straight to the mechanical pump.
Posted By: rapom
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 07:50 PM
I have a Carter pump plumbed before the mechanical and I ended up bypassing the mechanical because at speeds over 50 mph the car starved for fuel.
Posted By: burdar
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 08:25 PM
When I put a BB in my 91 Dakota, I left the stock electric pump in place. I only got a couple miles from home before the engine ran out of gas. Removing the electric pump from the system fixed it. Maybe a mechanical pump will pull through SOME electric pumps but they won't pull through ALL of them.
Posted By: gdonovan
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 09:42 PM
Quote:
I have a Carter pump plumbed before the mechanical and I ended up bypassing the mechanical because at speeds over 50 mph the car starved for fuel.
What kind of mechanical? I can hit about 85-90mph sustained speed before I see the O2 drop off.
Posted By: John_Kunkel
Re: Electric fuel pump push fuel through a mechanical pump - 03/05/15 10:15 PM
Quote:
Sorry to disagree, but the mech pump WILL pull through an elec pump. I have a Holley pump mounted by the tank that only runs when switched on.
As I stated earlier, not true on some pumps...Carters in particular.
Posted By: rapom
Re: Electric fuel pump push fuel through a mechanical pump - 03/06/15 12:07 AM
Just a new stock mechanical pump which worked just fine without the electric pump. I just got tired of prolonged cranking the car to start it. Kind of embaressing when at a car show.
Posted By: gdonovan
Re: Electric fuel pump push fuel through a mechanical pump - 03/06/15 12:23 AM
Quote:
Quote:
Sorry to disagree, but the mech pump WILL pull through an elec pump. I have a Holley pump mounted by the tank that only runs when switched on.
As I stated earlier, not true on some pumps...Carters in particular.
I have a Carter pump, no problem.
Posted By: Belvedere1
Re: Electric fuel pump push fuel through a mechanical pump - 03/06/15 10:22 PM
For the guys that have used this method of using both electrical and mechanical pumps, did it solve any vapor lock issues? Anytime my car gets to near 200 deg it runs like crap. The best we can buy here is the 91 octane junk.
Posted By: John_Kunkel
Re: Electric fuel pump push fuel through a mechanical pump - 03/06/15 11:19 PM
Quote:
Quote:
Quote:
Sorry to disagree, but the mech pump WILL pull through an elec pump. I have a Holley pump mounted by the tank that only runs when switched on.
As I stated earlier, not true on some pumps...Carters in particular.
I have a Carter pump, no problem.
You must have a vane-type pump, Carter gear rotor pumps are different:
"IMPORTANT NOTE:
When using a gear rotor type pump....
These pumps cannot be used as a secondary unit ie, on a dash switch. They MUST be wired to run continuously from the IGN circuit as your PRIMARY and ONLY PUMP.
This pump type uses a DRIVEN gear and a RING gear to create a positive displacement and force fuel through to the carb. The gearing is similar to your oil pump. They do NOT have any check valves like a mechanical fuel pump, thus if they aren't running, you cannot DRAW fuel through them via a mechanical pump, etc ( at least, enough to have the engine remain running)."
Posted By: DaveRS23
Re: Electric fuel pump push fuel through a mechanical pump - 03/07/15 01:28 AM
Quote:
For the guys that have used this method of using both electrical and mechanical pumps, did it solve any vapor lock issues? Anytime my car gets to near 200 deg it runs like crap. The best we can buy here is the 91 octane junk.
That is exactly why I first started experimenting with an electric pump. My car would run good MOST of the time. Only when it was hot out and I was at the track would it act up.
But when I installed the electric, I also went to 3/8 soft line to get the bigger ID and worked all the fittings to their largest possible ID. That increased my fuel delivery by over 50%.
I guess I just got lucky picking the Holly pumps that I have run. I have ran them on several different cars and always as supplement to the mechanical pump. Glad I didn't happen to pick a Carter. The Holley is so much easier to plumb, looks like.
Posted By: gregsdart
Re: Electric fuel pump push fuel through a mechanical pump - 09/13/19 10:22 AM
I saw this old post and thought of a couple of improvements that could be added.Jegs sells a 5psi pressure activated switch you can use to either open or close a circuit' . it could be plumbed into the fuel line by the carb and used to run a relay that shuts the electric pump down at 5 psi fuel pressure and above. Also to make the line from tank to mechanical pump less restrictive, I would try putting a T fitting before the electric and have the electric pump on another line with a one way check valve in front of it, then join the two going to the carb. A bit of extra complication, but if results are worth it to you,,,,,,,,,