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Technical 1940 flathead running problem

Discussion in 'Traditional Hot Rods' started by Motor, Sep 13, 2014.

  1. Motor
    Joined: Jan 2, 2009
    Posts: 3


    We have tried everything we can think of (including wholesale replacement of parts) and cannot solve the following. Car starts and runs great for a few minutes or about a half mile and then suddenly stops running. It appears to run out of gas but am not sure about that. We have replaced distributor, caps, wires, pump and pushrod. carb. harnesses, resistor, switch, and start relay. You can choke and restart car but it will quit again. You cannot catch it by pumping the gas. We have checked float level and installed carb spacer. None of this has changed or solved the problem. We have an inline electric pump used for start up. I need help.
  2. LSGUN
    Joined: May 26, 2007
    Posts: 1,338

    from TX

    Might be common sense, but did you clean the fuel tank? Maybe the fuel filter is getting clogged with rust/trash?

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  3. Larry Pearsall
    Joined: Apr 7, 2007
    Posts: 1,462

    Larry Pearsall

    Yrs ago I had a like problem with my 33 pickup.. Remove gas cap and see if it runs longer.. I had a gas line hose clamp (not leaking ) that caused the problem on top of tank. I had to remove bed to find problem, no problem after that..
  4. aaggie
    Joined: Nov 21, 2009
    Posts: 2,531


    Try running it at a fast idle in the driveway and see if it quits. It sounds like either a fuel starvation problem or a coil that gets hot and opens up. My guess would be fuel related.

  5. sixten
    Joined: Jan 25, 2009
    Posts: 11

    from sweden

    I had this problem on a Ford F1 truck, it was the gas cap, it let no air in to tank and its building vacum when you drive.When the car had stopp for a minute the vacum is gone and you can start the car.

  6. caton462
    Joined: Jul 17, 2013
    Posts: 176


    Remove the gas cap when this happens and see if it will run. We have seen a couple of tanks collapsed because of bad vent caps. If removing the cap doesn't allow it to run, loosen the line at the carb and see if fuel is getting there while cranking.
  7. fnjunk
    Joined: Jan 8, 2008
    Posts: 358

    from Australia

    Just had the same problem with a 59ab ended up being the condenser .

    Shit just got real.
  8. TraderJack
    Joined: Apr 10, 2008
    Posts: 330


    You say you have an inline electric pump for start up! What happens to the electric pump after you start the car?

    simple check, after stopped pull the carb covers and check for fuel by looking for accelerator pump and see if it is afuel problem, namely no fuel in carb. If fuel in carb it is electrical. pull sparkplug and check if sparking when cranked., If sparking, check for a bad coil that is opening up after the coil gets hot.
    And then pull gas line and see if the electric pump will pump a gallon of gas a minute. Not on the floor , but in a gas can. LOL Some times the electric pump may have a shut off if the gas is not re-circulating back to the tank.
  9. TraderJack
    Joined: Apr 10, 2008
    Posts: 330


    thinking a little more, it seems you have an inline electric pump, but you say you replaced the pump and pushrod, which seems to indicate that you use the electric pump to get gas to the regular pump to start the car. Now, an I am guessing because I can not see what is being done, the regular pump uses a vacumn to pull gas out of the tank and if you are putting pressure into the regular pump the regular pump might be stopping pumping as the valve in the pump is closed under pressure. (that is all conjecture as it has been along time since I worked on a flathead pump. So it may just be my old mind has gone away.
  10. F-6Garagerat
    Joined: Apr 12, 2008
    Posts: 2,652


    My brother just bought a 1970 ElectraGlide, takes it out, it stops running. Pops gas cap to have a look, plenty of gas. Starts back up, rides a mile, it dies. Pops the cap again, same thing. We are thinking the tanks have some crap in it, so start to pull them. The. P.O. Removed the "T" between tanks, one of which was a vent, and replaced with just hose and no "T". We put one back in along with a length of hose for the vent. Never does it again. Check the cap.
  12. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    Will the thing start and run after sitting for a while, then repeat the cycle?? If so, that is a classic description of a dying coil or condenser. Either will drop output as it heats up, work perfectly well when cold.
  13. 40fordtudor
    Joined: Jan 3, 2010
    Posts: 2,503


    I am inclined to agree with Bruce---I had this going on, way back when.
  14. Todd M.
    Joined: May 24, 2009
    Posts: 488

    Todd M.

    Vapor lock may be the culprit.
  15. flathead4dr
    Joined: Nov 15, 2010
    Posts: 15


    Not sure which dist. you're using, but if you haven't replaced the condenser, try that. These innocent looking little devils have caused many-a headaches !!!
  16. safari-wagon
    Joined: Jan 12, 2008
    Posts: 1,457


    Almost all of the condensers that are available are made in China. I've gone thru a few of them in the last couple of years.
    Hotrodmyk likes this.
  17. rfraze
    Joined: May 23, 2012
    Posts: 2,006


    Hope you have tried this. I'm thinking vapor lock also. No fuel in carb will answer that question. Then it's either fuel line heat or pump not pulling fuel thru electric pump. I bought a simple spark tester that goes on plug and fits in wire. Super easy to check spark.
    Joined: Jul 5, 2008
    Posts: 107


    How bout the carb spacer..maybe fuel is boiling? Or my guess condenser

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  19. King ford
    Joined: Mar 18, 2013
    Posts: 1,473

    King ford
    from 08302

    Cut your possible issues in half by duct taping a timing light to the windshield so you can see it flashing as your driving, if the motor stops running and the light stops flashing its spark, if you roll to the shoulder with the motor still turning(clutch out still in gear) but not running its fuel.......and what a lot of guys said...if its spark look at condenser and coil......just cause its "new" doesn't mean it's good!.....

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