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Flathead stock fuel pump won't suck.....?

Discussion in 'The Hokey Ass Message Board' started by Sixcarb, Feb 17, 2011.

  1. Sixcarb
    Joined: Mar 5, 2004
    Posts: 1,503

    from North NJ

    I have been through this before but seem to be getting a bit stuck on this one so hopefully I'm missing something and you guys may have some more ideas, motor is a 40 with a cast iron intake single carb. What I have done so far, tried 2 older pumps with no luck, checked the pump rod for length, replaced with new rod still didn't work, welded up an older rod to give it added height still no go, the rod is moving up and down enough to the point where it will pick the pump stand right off the intake. I also put a new line and fuel pump on as well. When I hand pump the fuel pump with a screw driver in a vise it makes suction with no problem, I tried putting the inlet line right in a can of gas and run the motor and still no suction, I tried filling the tank with air to get fuel up to the bowl still won't work, the only thing I didn't try was hand priming the pump on the bench which I have never had to do before. The rod is definitley going up and down quite a bit so I'm assuming the cam lobe is ok. Thanks.
  2. Destralo Roach
    Joined: Mar 27, 2006
    Posts: 521

    Destralo Roach

    I had the same problem, the lobe was just that much worn down, I made a block of plate in the pump so gas wouldnt go in to the crank case and used a eletrick pump, that way it still looked like the old pump worked.....Roach.
    Joined: Jun 6, 2005
    Posts: 1,887

    Member Emeritus

    IF you have suction by manipulating the pump, your pump functions correctly. If you check it with a fuel pump test gauge you should get around 10lbs vacuum on the suction side (marked in) and about 2-3lbs on the outlet pressure side. If you hook up the pump and it does not have suction capacity you have an air leak somewhere or an obstruction in the feed line. Do you have the correct fitting for the inlet line? Next have you back purged the inlet line to tank to determine if there are any obstructions. Now the simple question, do you have enough fuel in the tank to reach the fuel inlet tank pickup? In some cases the inlet tank pickup line is rusted off and the fuel level is below the connection so the line fails to pickup fuel.
  4. Sixcarb
    Joined: Mar 5, 2004
    Posts: 1,503

    from North NJ

    I tried bypassing the tank and main line by putting the short rubber inlet line right into a can of gas, that didn't work either, I'm thinking the only other thing to try is to put a dial indicator on the pump rod to see if I have enough lift coming off the cam, thanks for the replys.
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  5. Flatman
    Joined: Dec 20, 2005
    Posts: 1,975


    Sometimes the one way check valves inside the pump will stick shut from varnishing after sitting a while. A rap on the side of the pump with the handle of a screwdriver has freed them up for me in the past.

  6. big bad john
    Joined: Aug 11, 2010
    Posts: 4,727

    big bad john

    ......Same problem with my 36 flathead....had crap in the tank.....bought a new tank and line...but pump would not work....friend came over and pour gas down the carb so motor ran....finally enought pressure ....the pump started....he said it had to be prime....did'nt make sence to me, but been working for 3 years now....
  7. Smokey2
    Joined: Jan 11, 2011
    Posts: 920


    Re: Fuel Pump "won't SUCK!
    Electrick, is way to go..................Reminds me of Ole' Gal Friend, Same Problem!!
    I Sez, "Never You Mind!, I'll do it myself!"

    (Old Tennessee Trick!) Four Stars.
  8. Grab your compressors air hose, wrap some rag or something around the hose, stick in the gas filler hole and put some pressure to the gas tank. You can hear the gas going thru the pump and into the carburators. I have that often with freshly done engines when they are on the test run stand. The gas tank I use there has an air vent on top that I can connect to the air hose when some "help" is needed.
  9. Shaggy
    Joined: Mar 6, 2003
    Posts: 5,208

    from Sultan, WA

    So you are sure it is the right pushrod with the right fuel pump height? Arent some manifolds and stands different heights?
  10. Hoop-in-JAX
    Joined: Nov 7, 2007
    Posts: 184


    If your fuel pump has an attached glass filter/sediment bowl, check the bowl gasket for leaks. Common problem.
  11. Petejoe
    Joined: Nov 27, 2002
    Posts: 10,514

    from Zoar, Ohio

    Had a used pump stop. It pumped just fine by hand. Here the linkage was worn and would not work when installed but when doing it by hand I would compensate for the sloppy linkage.
    I realize you said you installed a new one but wanted to throw this out. Sounds like a vacuum leak either at the bowl or in the line. Unhook your fuel line and run it directly to a gas can. That should let you know if its really related to the new pump or the pump rod.
  12. Zombie Hot Rod
    Joined: Oct 22, 2006
    Posts: 2,451

    Zombie Hot Rod
    from New York

    Did you remove the screws and take the two halves apart yet? There's a rubber diaphragm in there. I've had a few pumps that had a little piece of "gook" in there keeping it from sealing properly.

    This might not be your problem, but it's worth a look.

    Also, try some starter fluid, or just pour some gas down the carburetor. Maybe your motor isn't turning enough with just the starter to get the gas flowing through the pump and into the carburetor.
  13. thunderbirdesq
    Joined: Feb 15, 2006
    Posts: 6,859


    Do you have a spare pump you can try?

    x2 on the glass bowl seal/tightness, if there's even a tiny leak or uneveness on the rim it's easier for the pump to suck air around the rim of the glass bowl than draw fuel up into the pump.

    Also, my roadster does the same thing if I run it completely out of gas. It won't siphon fuel up to the carbs by cranking the engine over, I have to prime the carbs and get the engine running for a few seconds in order for it to prime.

    Lift on the pump rod is somewhere in the neighborhood of .250". Even if the rod is lifting the pump off the manifold when not bolted down, it may not be actuating the pump with that travel. Though it sounds like you ruled travel out by now with your longer pump rod you installed.
  14. Sixcarb
    Joined: Mar 5, 2004
    Posts: 1,503

    from North NJ

    I already tried 2 older pumps and one brand new one, pumps make suction on the bench, I also put a can right next to the motor to bypass the main fuel line and gas tank. Tomorrow I'm going to get an accurate measurement of the lift of the fuel pump rod, I know I have the correct rod for the cast iron intake, the aluminum intake uses the shorter rod. As far as priming I ran the motor for about a minute and still no suction. If the cam turns out to be worn then decide to put a new bumpstick in or take the easy route and do a electric pump. Gotta love em.
  15. Ratroddude
    Joined: May 15, 2009
    Posts: 1,027


    If it won't suck , buy it dinner and a movie:D
  16. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    Stuff, all probably more elementary than this problem!
    Ford considered suction the key performance should pull 10 on vac gage, output 1 1/2--3 1/2
    Lobe lift: I have never found a proper Ford spec on this for external's in the .2--.25 range. The check in the book used a special gauge that referenced to the pump stand and so checked multiple factors.
    You have used an extra hose for tests, so leaks in flex or tank line are already ruled out
    Gasket under stand must be thin
    Bottom of pump stand must be flat...there is a warping issue on these
    Slop in linkage can kill the thing, and is difficult to check as pump off engine has lots of movement range and hand pumping compensates for motion in wrong part of range
    Leaks at steel lid/glass bowl (depending on type of pump) will also killit
    A possible check on worn linkage/movement of pump arm not in right range: Have someone hold down starter button, hold pump in place with no bolts, slide it down against pump motion about 1/2 bolt diameter. If it starts to pull, worn or incorrect linkage is putting pump motion in the ineffective part of its travel.

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