Fuel priming pump?

[56 Buick]

Hi, I am looking at fitting a low pressure fuel pump to prime the fuel bowls. Unfortunately when the car has sat for over a week, it is impossible to start the engine. It appears the fuel evaporates and the mechanical pump just can't move the fuel.

 

I am still going to use the mechanical pump to run the engine after it starts so this electric pump will just run for a few seconds to prime the carb. The electric pump will need to be a pump where the mechanical pump can pull fuel through even when the electric pump is not running. Also, it will only need to be a low 2-3 psi pump, that way no regulator should be needed.

 

I am interested to see if anyone has dome something similar? If so then what parts did you use and were there any issues encountered?

 

Thanks

 

Drew

[Machine Gun]

If your mechanical pump can't deliver fuel under the circumstances you've described, something is definitely wrong with your fuel delivery system. First, what do you mean by "impossible to start?" How much cranking before you give up on it? Sure, the fuel can evaporate at some point requiring longer than usual cranking, but a total loss of the ability to move fuel is not normal. A leak somewhere in the fuel line where air can get sucked in, a partial restriction (inline fuel filter, carb fuel filter if equipped, pickup tube or sock in the tank, etc.), and of course the fuel pump itself. I'm not suggesting that you give up on the idea of a priming pump, but I am suggesting that a priming pump should be used only as a supplement to a properly working fuel system after you've identified and solved the root cause of your issue.

 

I installed an electric pump this summer at the recommendation of a friend who lives at relatively high altitudes in New Mexico. I use it to supplement the mechanical pump to avoid or resolve potential vapor lock when traveling in hot weather at altitude (3,500 feet AMSL or higher), like when I was on my trip out west earlier this month. I switch it on and off as needed via a switch hidden under the steering column. If you eventually decide to install an electric pump to work in conjunction with your mechanical pump, be sure to get one that's a flow-through type, i.e. it will allow fuel to pass through unrestricted when turned off.

 

Let us know what you find.

[EmTee]

Extended cranking (30 ~ 45 sec.) to fill the fuel bowl isn't necessarily a bad thing.  It allows time for the oil pump to build pressure and get oil back into the bearings before the engine starts.  Just crank for 10 or 15 seconds and then let the starter rest for 10 seconds; repeat until it fires-up.  My '38 has an electric pump that I will use to prime the carb.  My Riviera and GP have only their mechanical pumps and I have done as I said above for five years so far with no issues.

 

Modern fuel will evaporate from a hot carburetor quickly.  I can literally hear it boiling when I place my ear next to the carb on my '38 after taking a drive...

[Frank DuVal]

Most of the little knock-box* pumps will allow the mechanical pump to draw through it with the knock-box pump not running. There are electric pumps that do not allow fuel to flow when off, check the specifications.

 

Yes, you do want to crank without starting for a few seconds to build oil pressure after an extended period of rest. Then flip switch to prime if necessary.

 

*Used to be squareish metal universal pumps that knocked loudly while operating, now plastic and roundish.

[Dan O]

I put a small inline electric fuel pump right off my gas tank to push fuel to the rebuilt mechanical pump in my '49.  It's a Chinese 6 volt pump and it works well.  I have a momentary switch mounted under dash.  I let mine sit for weeks and then the bowl empties.  This makes it easy to fill and not drain down that precious six volt battery reserve and also avoid heating up my starter and wires.  I put a hotrod-type clear inline filter back there in front of the electric filter as well.  I also keep a can of starter fluid handy and use it on initial startups.  It sure gets her going without a lot of hassle.  Once warmed up, she starts good thereafter until I put her back to bed.

[60FlatTop]

On 10/29/2022 at 7:26 AM, Machine Gun said:

If your mechanical pump can't deliver fuel under the circumstances you've described, something is definitely wrong with your fuel delivery system.

I am on board with that. My cars sit fairly long periods, 2-3 weeks or more. I alternately crank and pump a consistent and predictable number of times for a start. Step one would be isolating the fuel line from the tank sending unit to the fuel pump inlet. Pressurize or pull a vacuum on that. Many cars have a flexible hose at the tank that rarely gets checked. I bet I could go to a Buick meet and walk away with a handful of 50+ year old rubber hoses.

 

Next check the operation of your choke system in including the pull off and its diaphragm if it has one.

 

And check the distributor advance plate to make sure it moves freely. If you are trying to start with a little extra advance it is going to exacerbate other issues.

[EmTee]

The shop manual will provide a specification for fuel delivery.  Disconnect the fuel line from the carburetor and route the output to a suitable container.  Crank the engine for the specified amount of time and compare the volume delivered to the specified amount.  If the volume delivered is low, that could indicate a bad pump, or a fault upstream in the fuel line.  That's where the checks mentioned above by Bernie can help isolate the root cause.

[Gary W]

I installed an electric "priming pump" for the same reason.    After sitting about a week, starting was a long cranking experience.  

 

Follow this post for the entire install:  Just touch the arrow in the upper right corner.

 

 

[56 Buick]

Hi all, I hear you re possible issues with the fuel delivery system and I will check as suggested. I have never continued to crank the engine for 30 seconds or more as I have been concerned with the battery and straining the starting circuit but I can also try and see. However, another reason for the priming pump was to counter the vapour lock that can occur. The car can be difficult to start again while hot after a drive. Gary's link above to his work and write up is really great and informative. Thanks to all.

[60FlatTop]

2 hours ago, 56 Buick said:

The car can be difficult to start again while hot after a drive.

That is a good reason to check the vacuum advance for free action. Probably one of the best reasons to check it.

[56 Buick]

Thanks. I will connect a vacuum pump and see if the distributor plates moves. Is the plate supposed to move and hold at the advanced position or will it rather be momentarily?

[old-tank]

6 hours ago, 60FlatTop said:

9 hours ago, 56 Buick said:

The car can be difficult to start again while hot after a drive.

That is a good reason to check the vacuum advance for free action. Probably one of the best reasons to check it

On my cars it's because of the fuel has boiled or percolated into the intake manifold and you have a flooded engine.

[Bloo]

11 minutes ago, 56 Buick said:

Thanks. I will connect a vacuum pump and see if the distributor plates moves. Is the plate supposed to move and hold at the advanced position or will it rather be momentarily?

You should be able to move it all the way until it stops with the vacuum pump. It should stay there until you release the vacuum. Then it should go back without sticking when you release the vacuum.

 

[56 Buick]

1 hour ago, old-tank said:

On my cars it's because of the fuel has boiled or percolated into the intake manifold and you have a flooded engine.

So how do you get the car to start in this circumstance? After the car has been driven and the engine will not start again, I have always had to wait until the engine cools down after which it then will. But I have only ever assumed it was vapour lock and not tried much else.

[56 Buick]

1 hour ago, Bloo said:

You should be able to move it all the way until it stops with the vacuum pump. It should stay there until you release the vacuum. Then it should go back without sticking when you release the vacuum.

 

Thanks, will try this.

[EmTee]

8 minutes ago, 56 Buick said:

So how do you get the car to start in this circumstance?

If it is really flooded, you should hold the throttle open while cranking the engine until it starts and clears the excess fuel.

[56 Buick]

Thanks. I had heard it is often the fuel boiling away down near the mechanical fuel pump but I will give it a try and see if it starts.

[Frank DuVal]

On 11/3/2022 at 10:36 AM, 60FlatTop said:

That is a good reason to check the vacuum advance for free action. Probably one of the best reasons to check it.

???  While checking the vacuum advance is a good idea during a tune up, just why would a bad vacuum advance cause hot starting issues? OK, if the starter drags as if the timing is advanced, I can see that. Does the starter drag when starting hot, 56?

 

Yes, hot start usually requires holding accelerator pedal near or on the floor.

Edited November 4, 2022 by Frank DuVal (see edit history)

[60FlatTop]

Some cars have a thin pad the the breaker plate rides on. The pad is a wick for the drops of oil added through the lubrication cup. When anyone is looking at a 60-70 year old car they have to think about what has been neglected. Those pads can dry out completely. Other forms of breaker plate lubrication can dry out as well.

 

Many times I have heard the story. My car starts fine when it is cold. I drive a couple of miles to the gas start and when I restart it the engine grunts like it has a low battery or the starter drags (drags on what? The brushes?)

The tension on the advance, the diaphragm spring, or whatever pulls the plate back to the retarded position can creep back while the car sits overnight. But the time to pump and pay for the gas may not be enough. The owned is stuck at some level of advance trying to start. The plate did not have time to creep back. Left to the field of speculative diagnostics all kinds of things can be imagined. That is where the "I reckon" diagnostics come in.

 

I know people who are afraid to take the breaker plate or the distributor out of the car. Some remember a car that never ran again after they did. Lube pad or bear after half a century it probably needs a good cleaning. I have seen cork pads that looked like thin black dry paper.

 

To test all you need to do is rotate in the advance direction. The plate should return in a snap. Slower needs attention.

 

I have been able to revive the cork by massaging fresh oil into it with my fingers

[JohnD1956]

For the pad Bernie mentions there is a hole on the breaker plate for that oil. I used a few drops of marvel mystery oil the first three times after @jackofalltrades70 told me about it. Last time I used some straight 30 weight, non detergent.  I believe it made a big difference.