Does running an electric fuel pump cause fuel restriction?

[Laughing Coyote]

As some of you know I received a 1973 Corvette from a generous neighbor. The car has a 454 engine with a Quadrajet carb. After the car sits for a few days it takes a lot of cranking of the engine to finally get it to fire off. Once running it runs good. I did some research and it seems to be a problem for these carbs on hot days. The fuel bowl is very small and fuel evaporates quickly. I'm thinking of adding an electric fuel pump to act as a primer pump so it will start easier. My question is once the car is running and I turn off the electric pump will it have any restriction on the amount of fuel going down the line to the mechanical pump? Has any of you experienced any fuel issues by doing this? 

[PONTIAC1953]

no fuel issues with the electric fuel allowing fuel to pass through to the mechanical fuel pump when the electric pump has been turned off.

[edinmass]

First off……not all electric pumps can be pulled through with a mechanical pump. Also, proper installation means NO rubber lines at all. Third, you must NOT wire it to the ignition circuit, as a pump draws way too much amperage and will under volt the ignition system and overload the circuit and switches. So adding electric pumps are often a good idea. Doing it correctly is difficult and time consuming. The car is suffering from “hot soak” where the gas boils out of the bowl from high under hood temperatures and modern fuel lower boiling point. Cutting into the factory lines on a cool car is not what I would do in most cases. I would ask the guys in the Vette club what is the acceptable solution. I’m thinking if it was my car…….I would live with it.

[37_Roadmaster_C]

14 minutes ago, PONTIAC1953 said:

no fuel issues with the electric fuel allowing fuel to pass through to the mechanical fuel pump when the electric pump has been turned off.

Ed types faster than me...

 

Slow Down Here....   This depends on the type of electric pump!  Some will GREATLY restrict fuel flow when not running and some will pass fuel with minimum restriction. I do not know which specific pumps will work as you want, but someone here will jump in with answers. Another sure way to avoid this problem is to add a check valve to bypass the electric pump when it is turned off.

Edited July 19, 2023 by 37_Roadmaster_C (see edit history)

[f.f.jones]

I have a 455 Buick with he same problem, otherwise it runs well. I'm anxious to hear a definitive solution to this Quadrajet problem with recommended  electric fuel pump brands mentioned.  

 

 

[Hans1965]

I am using an electric pump on my 53 Buick Roadmaster and I am very happy with it. It is a low pressure pump that adjusts to the output needed, no back line to the tank needed, no pressure regulator. It simply adjusts to the consumption of the engine. It runs permanently. When I put the ignition on I hear it running quickly and as soon as the 'clicks' more or less stop I know the gas line and carburetor are filled and the engine starts at the first attempt. Never had vapor lock issues, too. My impression is it draws very little current. When you look for such pumps you mostly find the cheap Asian build ones. I tried that once and it leaked gas out of the housing. I through it out of the window the same day. I now have a Hardi pump installed. Build in Germany, hand made, with local components, costs three times as much but peace of mind. You get what you pay for. I never found out if they can be stopped and there is still gasoline flow possible. I still have the mechanical pump installed. The electrical pump is installed very close to the tank. I am going to install one on my 49 Buicks as well. There I have to run the starter for 30 sec untill the mechanical pump has filled the carburetor again, quite annoying. I have been just too lazy. 🤣

 

https://www.hardi-automotive.com/en/

 

I am not associated with this company, just a very happy customer!!!! Only posting this because it might help somebody. 

 

PS. I just got feedback from a Hardi representative, that they can be used as primer pump only, when you switch them off, the mechanical pump can take over and pump through the Hardi pump. Fantastic. 

Edited July 19, 2023 by Hans1965 (see edit history)

[edinmass]

 

Besides all I listed above......using properly sized and flowing fittings and adaptors are extreamly important....and 80 percent of pump installs have restricted or under sized fittings..........just more to look out for.

[60FlatTop]

If you flip that Q-Jet upside down you will see two plugs right in the center of the body. Thirty years ago I was replacing them on Cadillacs of your Corvette vingate. That would be the first place to check. It will also cause hard starting when they are hot when fuel drips into the manifold.

[Laughing Coyote]

42 minutes ago, 60FlatTop said:

If you flip that Q-Jet upside down you will see two plugs right in the center of the body.

The plugs have all been sealed so there is no fuel dripping from them. The car has a heat displacement shield under the carb to cut back on the boil off. I just need to be able to fill the bowl up so I'm not cranking the starter for 4 minutes until it fires. It wouldn't be used all the time, just to prime the carb.

[Avanti Bill]

Try rebuilding the fuel pump.  It may be that there is a check valve leaking back which also diminishes the output of the pump.  I think people are too quick to go to an electric fuel pump when fixing the original is a better solution. 

[Laughing Coyote]

3 minutes ago, Avanti Bill said:

Try rebuilding the fuel pump

The fuel pump is about 3 years old and the car runs great once it's running. The fuel pump has 3 fittings. One for fuel in, one for fuel to carb, and one to return fuel to the tank. There's no sign of leaking from the weep holes. Evaporation is a big problem with the Quadrajet carbs. I appreciate everyone's input so far.

[60FlatTop]

I have had the flex line at the fuel tank suck air but not drip fuel. On an older car with a glass filter bowl you can sometimes see bubbles. On a newer car it can be overlooked.

[dodge28]

Laughing Cayote, You posed a very interesting question . I am exploring the possibility of  installing an electric fuel pump to fill the vacuum  pump on my 1928 Dodge Senior. I need advice . Now , after reading all the comments I am a little more informed.  

[JACK M]

I keep a squirt can of gasoline in my garage.

I would have to buy and install to many electric pumps if I was wanting all of my cars to start right up after any prolonged rest.

It's easy to open the hood and drip a bit of gas down its throat. At least on the down drafts.

There are occasions when I could use an electric pump to overcome the vapor locks. (Time to discuss clothespins again?)

[Pfeil]

If a Q jet, 4GC, ABF, or even a monojet sit for more than a couple of days the float bowl will be dry. So, three cars of mine have one, a Q jet, two, a mono jet and three, a 4GC. They all seem to take about as much time to fill with fuel as it takes their oil pumps to pump pressure to 40 PSI and at that time all engines will sputter. This happens in about 8-10 seconds of cranking and in that cranking time you never touch the throttle (unless you would like to wear out the accelerator pump). Now that the engines are OIL PRIMED and FUEL PRIMED- two squirts on the accelerator and they fire right up. The only other car that I have with a carburetor that can pull up fuel faster is one of my VW beetles because it has a manual choke, when you pull that choke closed the engine vacuum while cranking helps the pump along by negative pressure.

 

If you are having hard starting cold because of lack of fuel to the carb the first thing to do is check not only the fuel pressure but how many gallons per minute it is pumping. As pumps age they don't pump as well so check that first. Choke closed?

Original poster didn't say if this car is A/C equipped. Many GM cars are equipped with a fuel return line which helps the vapor lock problems. It recirculates cool fuel from the tank to the carburetor. If you don't have one buy yourself a GM AC filter that has the return built in and all you need to do is run a line back to the tank. If your car is a AACA show car I don't know if they would deduct points, but if it means being stuck or pulled over on the side of the road with the hood up instead of being at the cruise night you're supposed to be at......well!

Adding an electric fuel pump is a Band-Aid fix masking the real problem. BTW, I have known many guys still on the side of the road mind you that have an electric fuel pump and still have vapor lock because they don't have that return line. Seems always a hot late afternoon/early evening at a real cruise night where the cars are in parade mode driving around the town square bumper to bumper, they drop off one by one.

[Laughing Coyote]

31 minutes ago, Pfeil said:

If you are having hard starting cold because of lack of fuel to the carb the first thing to do is check not only the fuel pressure but how many gallons per minute it is pumping. As pumps age they don't pump as well so check that first. Choke closed?

Original poster didn't say if this car is A/C equipped.

The choke is closing and it's an A/C car with the return on the bottom of the fuel pump. I will have to put a gauge on the fuel pump and see what it's delivering. I have to cycle cranking it 5 or 6 times at about 15 seconds each time. Once fired it does stumble until it gets warmed up. 

[Pfeil]

32 minutes ago, Laughing Coyote said:

The choke is closing and it's an A/C car with the return on the bottom of the fuel pump. I will have to put a gauge on the fuel pump and see what it's delivering. I have to cycle cranking it 5 or 6 times at about 15 seconds each time. Once fired it does stumble until it gets warmed up. 

I did a test on a friends Avanti- 305" w/ Qjet. Hard start after sitting cold for a couple of days. OEM original pump. I can't remember how many GPM it produced, but I do remember somewhere about 1-3/4 or 2 psi. N/G replacement necessary. 

Think about this, All the other carbs I mentioned have larger float chambers that Q'Jet, so it takes less time to fill and is ready to go before the others.

BTW don't ever let anyone talk you out of a Q-jet. It's one of the best carburetors ever made, and for many reasons. I just wished they invented them earlier. Great performance, variable engine displacement ability carb, excellent high mileage carburetor with high velocity primaries, and a super carb. for road racing due to its anti-sloshing capabilities of its float in high G load side load turns. I've never had one nose over on me in a critical moment on the track like you would on other carburetors. 

Edited July 19, 2023 by Pfeil (see edit history)

[Pfeil]

I should have mentioned this before. Make sure your sock on the end of your fuel tank pick-up tube is in good shape and not clogged. 

[Laughing Coyote]

40 minutes ago, Pfeil said:

Make sure your sock on the end of your fuel tank pick-up tube is in good shape and not clogged. 

The entire tank was removed and pressure washed out, inspected and is totally clean. The sending unit sock was also cleaned and checked. New fuel hoses were installed from the tank to the hard lines. The carb does operate great when the car is running. It's jus the hard start issue after sitting. I will be checking the pump output first and go from there. Everything else I have come across so far has been neglected or poor maintenance practices.

[arcticbuicks]

most Q jet carbs have the paper filter element behind large nut where fuel line connects to carb......with a spring to hold in place,you could check to see if yours has the filter with check valve in it ......not all are check valve type to prevent fuel drainng back.......or if you have check valve type in your carb.....may be time for new one 

[Laughing Coyote]

10 minutes ago, arcticbuicks said:

most Q jet carbs have the paper filter element behind large nut where fuel line connects to carb

Mine has the pressed brass one in it. I have a new Wix one, but not sure if it has the check valve in it. 

[Pfeil]

3 hours ago, Laughing Coyote said:

Mine has the pressed brass one in it. I have a new Wix one, but not sure if it has the check valve in it. 

There has been a fair amount of Q jets thrown away because of that fuel filter location, whether or not it's a front inlet like Buick, Oldsmobile or Pontiac or a side inlet like Cadillac, Chevrolet. The truth is, unscrewing, screwing wears those fine threads out. On my cars all of those type of filters are removed and an inline filter is in its place. That also includes a Monojet.  

[EmTee]

After sitting a few days my '67 Riviera typically requires three 10 ~ 15 second starter cranking cycles to start.  As Pfeil said, by the time fuel arrives the oil pump is also making pressure.  Assuming nothing changes, I'm perfectly content with the situation.  Worst case scenario is I wear out the starter prematurely.  Oh, and it's probably easier to fix the starter than it would be to add the electric fuel pump... 

[Ovalrace25]

7 hours ago, dodge28 said:

Laughing Cayote, You posed a very interesting question . I am exploring the possibility of  installing an electric fuel pump to fill the vacuum  pump on my 1928 Dodge Senior. I need advice . Now , after reading all the comments I am a little more informed.  

Careful! If you put an electric pump on your vacuum pump system, PLEASE use a push button and not a toggle switch! The push button will allow you to put enough fuel into the vacuum pump tank so you can start the engine. Push button, count to five and release. I dont want to hear about any fires because the electric pump overfilled the vacuum pump and gas went all over the engine! 

[Robert G. Smits]

I have had a rotary pump mounted close to the fuel tank on my 41 Cadillac for 15 years.  Use only for priming and the rare vapor lock on a hot Texas day(104 today).  If you want a unhappy wife try experiencing vapor lock at a busy intersection during 5 o clock traffic.  Been there.

[Pfeil]

I think that instead of worrying about how long it takes to prime the carburetor on an engine that hasn't been driven in a few days-weeks- months, the important priming is oil priming the engine. I think on my cars engines they both oil/fuel systems seem to be ready about the same time.

 Back in 1973 I had a Plymouth Signet with a 30-D 225 six. Those rods would rattle overnight cold-so I would crank till the oil pressure light went out before I started it-easy to just don't touch the gas pedal until the o/p light goes out. I couldn't get rid of that car fast enough. Those rods must have had at least .004+ clearance. Must have had 4 cans of STP in it. Even so it still sounded like Buddy Hackett trying to talk with a mouth full of marbles.

Edited July 20, 2023 by Pfeil (see edit history)

[mrspeedyt]

I blame this modern gas. seems to evaporate pretty darn quick compared to old school gas. 

 

I don't mind cranking 15 20 seconds or even a half a minute because I also believe having a pressurized oil system doesn't hurt when the car does start.

[John348]

7 hours ago, mrspeedyt said:

I blame this modern gas. seems to evaporate pretty darn quick compared to old school gas. 

 

I don't mind cranking 15 20 seconds or even a half a minute because I also believe having a pressurized oil system doesn't hurt when the car does start.

Very true, when I owned my Cosworth Vega and located the Weber Carburetor set-up I had to change the electric fuel pump to a lower pressure from the one required to operate the EFI. I used an oil pressure switch that had both N/O and N/C contact positions. The oil pressure switch is the safest way to control an electric pump, if the engine shuts down you want that pump to shut ASAP. Some guys wired in a bypass in for initial start up 

[Gary W]

I installed an accessory electric pump to prime the carburetor when the car sat for more than six days.  

I now push the button under the dash for about 30 seconds to fill the carburetor bowl and she fires right off.

The original fuel pump works fine the rest of time and it draws fuel through the electric pump just fine.  No issues at all. 

 

Here's how I installed the inline fuel pump.  As I stated, I use it only to fill the carburetor prior to starting, so I installed a momentary push button under the dash.

 

Step-by-Step install:

 

 

[Hans1965]

Gary, you are a real mechanic. Very impressive work. You are cutting no corners like I try to do all the time. And on top you document your work so well for others. Just amazing. Thank you!