Can it be just a loss of prime?

So I just got my 1950 Pontiac back that I sold 7 years ago. The car had been sitting for awhile. It still has the straight 8 flathead. When I poured fuel in the carb it fitted right up but would die after it burnt that fuel. I had the fuel feeding into the mechanical pump from a gas jug. Reason was one the fuel was old that was in the tank and the original rubber house was rotted and broke on the trailer ride home. After doing thus several times with no luck I checked the fuel line on the inlet side of the pump and it was dry. It showed no signs of pumping any fuel. So after reading on here I went out and bought a electric fuel pump (not yet installed). The pump on the car looks fairly new but I am unsure of it's history. My question is could the pump just need to be primed?

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Fuel line plugged? Carb float/needle stuck is more likely.

 

Pump has probably died do to the length of time it sat and possibly the affects of the new gas.
An electric fuel pump should do the trick.
Is it 6 or 12 volt now, the car that is?
Be sure to use a regulator and set it up for not more than 3 lbs. pressure.
Good luck
KK

 

The previous owner mentioned he thought he had trash in the carb. So that would keep the fuel pump from pumping fuel?

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Not ****ing fuel?
Well any hole in the hose - think when your soda straw has hole in it- will prevent it from ****ing fuel. Also, the inner pump working could be fouled or dry rotted .

 

I put a new hose on the inlet side of the pump and put that hose into a gas jug. I then took the outlet line off. I was just trying to see if that pump would pump any fuel. But both sides remained dry.

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Any chance the hoses are reversed ?

 

Anything is possible I guess. I will check in the morning just to make sure. I bought a Airtex fuel pump today if all else fails.

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prime the pump, dry valves dont work too well, bit of fuel down both sides.

 

Could also be the small hose from the top of the tank to the fuel line is rotted. Have had that happen several times with sitting autos. Trash in the crab would not matter.

 

Right now the fuel tank is out of the equation. I'm feeding the pump out of a gas jug.

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If the pump is good, it should **** fuel from a jug quickly, and send it up to the carb. It's likely that it is bad, since it's old and then sat for years with old gas in it.

 

put the hose in the jug. pull the line from the carb off and **** the fuel from the jug thru the pump until you get a small sip in your mouth. Spit it into the carb and re connect the line. pump is now fully primed.

You could use one of those plastic vacuum hand pumpy things if you don't have a mouth.

my 2¢.

 

Well I did some checks and this is what I came up with. Lines are hooked up correctly. Decided to check the strainer in the carb to see if any fuel was making it and this is what I saw.......gasket sealer and a small rock. Cleaned it all out and primed the lines as Jokester suggested. I also put a little gas into the carb. The engine initially hit but nothing. Did this about 4 or 5 times with the same result. (only primed as Jokester suggested once) Pulled the line by the fuel pump and nothing, lost prime.

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A mechanical fuel pump has a diaphram that is likely shot. No matter what you do it is not going to pump fuel.

Stop worrying about the "prime". A good fuel pump will draw fuel and push out air, priming is not a concern.

Replace it or use your electric pump and you should have no problems with a clean tank and good fuel lines.

 

Sounds to me like rebuild /replace the fuel pump,carb,hoses/clean tank.

I had Airtex fuel pump on my rod and replaced two within a few months.

Read the online reviews for them,they get bad reviews.

I went back to a mechanical pump

 

Does a Pontiac straight 8 use a push rod of some sort to actuate the fuel pump? It could be sticking in it's bore and not actually moving the pump lever.

Is your gas jug setting anywhere near the level of the fuel tank? If the jug was on the ground and you have the hose routed up over the fender and back down to the pump it may not make enough vacuum on the inlet side of the pump to draw fuel that far.

Hook up a small remote fuel tank somewhere above carburetor level and let it gravity feed the carb. Route the pump outlet back into your gas jug. If you get things running for a few minutes the pump might start working again.

Hook up a vacuum gauge to the pump inlet and spin the engine over. I'd guess that you should see some movement of the needle if the pump's working. Even if you don't have a vacuum gauge put your finger over the pump inlet and you should feel a slight pulse when cranking the engine.

Check your oil for being over full and for the smell of gasoline. A ruptured pump diaphragm can allow gas to get into the crankcase.

 

Fuel pumps are self-priming.

 

Your pump is dead !! Shoud be driven drictly off the cam. Hook up the electric and don't waste anymore time on that old mechanical pump.

 

Ok so I think we are all in agreement the pump is dead. Now for the old faithful question. I already have a Airtex electric pump (uninstalled). I called today and found a new mechanical pump for $150. I understand I can rebuild the one I got. So with this opportunity do I install the electric pump or fix the mechanical? Thanks to everyone who has replied.

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Some guys would go with the electric, others the mechanical. Seems you've already made up your mind. Which do you want to run?


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I hate the idea of a toggle switch and premature failure from some **** pump. But don't won't to miss a chance to move the car in a better direction. Now to figure which is the best. I love the idea of stock.

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I'd run the stock one if I could.

Electrics aren't bad, it's just a few more things in the chain that can go wrong. The cool thing about this old stuff is that they are free of these "chains that can go wrong".

If you wanted electric, I'd wire it with a momentary on ****on to the relay trigger and a oil pressure switch to the relay trigger. That way you can run the pump when ever you want but by holding the ****on. The oil pressure switch closed will keep the pump running as long as the engine is running with oil pressure. It's all automatic and Mom can handle it.

 

Keep both. I like the way an electric fuel pump fills up the carb quick when you run out of gas because the gas gauge is broken!

 

I run mechanical pumps in all my old cars. They have made it this far on them, I don't see a reason to change up.

 

here is a picture of a fancier combinatoin vacuum/fuel pump as used in 1955 Pontiacs.
I think if there is junk under either of the valves or the diaphragm is torn it won't pump fuel.


http://pontiacsafari.com/55/ShopManual/6B - Fuel and Vacuum Pump.pdf

 

Thanks guys. Stock it will be.

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I had a unit that a previous owner had converted to electric pump. That lasted a year and when it fried, I went back to the mechanical pump. No probs since.

 

don't forget with a mechanical pump , the lines must be hole free the whole length from the inside of the tank to the pump . I found pinholes inthe backside of my fuel lines they looked great on the front , but dirt was between them and the frame and rotted them out .

 

How did this turn out for you? I have a 49 Pontiac with the straight 8 and the mechanical fuel/vacuum pump. I rebuilt it a few years back and have not had a problem with it. If you can, get your hands on the shop manual as there are a lot of good tips in there. Take good notes and pics when you dis***emble...

One more thing, there are a ton of screws and lock washers that hold the pump and vacuum diaphragms in place!

Chris


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