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flathead stumbles on acceleration

Discussion in 'The Hokey Ass Message Board' started by walls, Aug 29, 2010.

  1. walls
    Joined:
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    Green Lane PA

    walls Member

    I need a little help with a stock flathead-single 94-stock distributor, mech fuel pump in a 50 ford I just bought.

    The carb has been cleaned, has stock jets and has a new fuel filter. The accelerator pump works. I haven't checked the timing yet or the points but i suppose that's my next stop.

    The car hesitated when stepping on the gas. If I step lightly on the gas, it will make it up through the gears (slowly) but, if I stomp on it, it continues to stumble. I thought it was the float level. I set it to the correct level (it was a little low) and put the throttle plate lever linkage back in the middle position (it was in #1).

    I hopped in the car and went down the road. All seemed well, the car accelerated perfectly. I thought I fixed the problem. I parked the car for about 5 mins, went back to the car and I'm having the same problem. The only thing that could have changed in that time would have been temperature and possibly the gas. Even though i have a filter I don't know the condition of the tank.

    One other weird detail, someone wired in an electric fuel pump w/ a switch. I have no idea why.

    Any thoughts?
  2. 35desoto
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    35desoto Member

    It has a fuel starvation problem - sounds as though the accelerator pump on the carby has a blockage somewhere that clears at times and then re blocks its self . Your symptoms are in keeping with a lack of fuel at a time when the vacuum falls and there is not enough of a "signal" for the engine to draw more gas and the engine needs more gas - which it is not getting. Gotta say - head back to the basics and clean every little orrifice out
  3. blown49
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    West Union, OH.

    blown49 Member Emeritus

    Could be the flex fuel line at the inlet to the fuel pump inlet has collapsed or pluggage in the fuel line from the tank. Try running it with the electric fuel pump and see if that does anything for it (maybe that's why it was installed.)

    I'd also change the condenser NAPA IH200 if 6 volt or FA66 if 12 volt.

    Jim
  4. two coupes
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    two coupes Member

    Have you checked the vacuum-assisted power-valve?
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  5. chappys4life
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    chappys4life Member

    Have you checked the vacuum module on the distrubtor? They go bad and cause those symptoms.
  6. walls
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    walls Member

    How do you check the power valve? I'm assuming that since it's not at WOT it's not the valve. The plugs are not fouled either.

    I have a manual on order but, in the mean time, how do you check the vacuum module? I guess you're saying it's possible my timing is off because my vacuum advance is not working?
    Is that something that can work one minute and then not the next?

    I have a few free minutes, I'm going to go out now and take a look at the car.
  7. RuFFDaWG
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    RuFFDaWG Member

    Had problems with my single carb stock flathead - a Holly/Ford 94. Would surge at idle, have a miss, run rich, etc. Took the carb top back off and adjusted the float level again based on the specs in our rebuild kit. This seems to have eased or cured the problem in our case.
  8. walls
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    walls Member

    I just took it out for a spin again. It sputters in 1st, is fine in 2nd in mid rpm and seems to run fine in 3rd.
    I'm going to pull the carb and clean it then go from there.
  9. 35desoto
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    35desoto Member

    yOUR SYMPTOMS ARE STILL LEANING TOWARDS A LEAN FUEL MIXTURE - COULD BE A VACCUM LEAK FROM A DISTRUBUTOR ADVANCE DIAPHARM LEAKING OR THE CARBY STILL OFF TUNE SOMEWHERE - KEEP LOOKING - ITS THERE SOMEWHERE.IN FIRST GEAR YOU HAVE THE HIGHEST DEMAND ON THE ENGINE AND AS YOU GO UP THE GEARS THAT LOADING ALTERS AND THE ENGINE DOES NOT RESPOND THE SAME HENCE YOUR "MISS" DISAPPEARING AS YOU CHANGE UP A GEAR
  10. chappys4life
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    chappys4life Member

    I have a manual on order but, in the mean time, how do you check the vacuum module? I guess you're saying it's possible my timing is off because my vacuum advance is not working?
    Is that something that can work one minute and then not the next?

    I have a few free minutes, I'm going to go out now and take a look at the car.[/QUOTE]

    I was told a way to test them is to pull the vacumm line and have someone rev the motor as you blow into the line. If it runs smooth for the test your unit is bad. If your not sure about the age of the distrubtor its a 20 part and really takes a lot of guess out of your problem.

    What that part does is control your advance, when you get on the gas to accelerate and there is no vacumm pressure it advances the timing. So when your getting on it and it stumbles thats a good part to check. Had the same issue with mine until I replaced that part.
  11. AJofHollywood
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    AJofHollywood Member

    I had a similar problem, resolved by replacing the power valve accessible between the bottom and middle segments of the carb.

    I rebuilt my the 94 myself, it was a pretty worn out carb to begin with. The power valve would blow-out occasionally.

    Later I rebuilt a replacement 94 after being fed up with the worn and leaky one. The replacement was a very good core --no leaks & blown valves since!
  12. walls
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    walls Member

    I rebuilt the carb last night. Everything looked good except there was teflon tape on the power valve. I haven't had a chance to drive it but, I'll post the results when I do.
  13. LUMBERJACK 50
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    LUMBERJACK 50 BANNED

    power valve.....its screwed into the body of the carb on the underside between the base and body.. if it were starving for fuel it would do it all the time...ITS THE POWER VALVE. all it takes is to cough a 94 once and that valve is gone. to adjust your float make sure the top of the float is level with the top of the bowl. is some case's just slightly less the top of the bowl.
  14. medicinal_marinara
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    medicinal_marinara Member

    The teflon tape is a clue... the power valves that properly fit the 94 aren't available any more. The ones for the 4 bbl holley fit in the hole, but aren't machined to seal right. That's what the tape was for.

    The problem is, teflon tape tends to slough off little hairs and pieces after a while, and clogs stuff up. Either use pipe dope or machine the power valve to fit right.
  15. 35desoto
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    35desoto Member

    Holley power valves are notorious for "blowing" and then there is no lenght of problems to fix - cause it can't be fixed till the power valve is renewed
    Teflon tape eventually dissolves in our fuel down her - something called aromatics - so yes it will disintergrate and block other orifices etc
    Sounds as though you have found the problem and it all adds up - good luck in fixing the power valve correctly
  16. lasctchance
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    lasctchance Member

    i bet the power valve...
  17. bowtie40
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    bowtie40 Member

    I hate to beat a dead horse, fuel delivery... either acc. pump, or power valve
  18. tjet
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    tjet
    ALLIANCE MEMBER
    1. Early Hemi Tech

    Disconnect the distributor vac advance & cap off. Drive it & see how it does.
  19. walls
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    walls Member

    The rebuild kit I bought was from Mac's. Does anybody know if they come with the proper type power valve? It seemed to seat just fine.

    I know there is a couple threads showing the differences between the new and old style but, I couldn't find them. I'll look again after I get home from work tonight.

    Is it common for people who use 94's to carry extra power valves with them in case of similar problems?
  20. Teep
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    Teep BANNED

    GET A STROMBERG 48 or 97!!!! i had the same problem with power vales and i went through 4 94's before i decided to spend the cash and get some strombergs. just my 2 cents...
  21. walls
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    walls Member


    That might be my next move. I've already got a new distributor ordered from bubba. I was going to eventually run a 2x2 setup so, the distributor was the next step whether I ran 94's or 97's.

    I rebuilt the carb and replaced the vacuum advance. No luck.

    I works great on idle and to about quarter throttle. At this point I still can't rule out the carb for absolute certain but, with the new distributor coming, I think I'm going to start there.
  22. StrickV8
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    StrickV8 Member

  23. forty1fordpickup
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    forty1fordpickup
    ALLIANCE MEMBER

    There are two check valves in the accelerator pump circuit. A needle type under the nozzle assembly and a ball type under the plunger. If either one is is hung due to dirt you will have stumble on acceleration. The are some posts about the 7.5 power valve that comes with the rebuild kit opening too soon. You may want to try a lower value, say 6.0 or 6.5 with a single. I'm running 59A with 2 94s on an Offy regular dual with good response. These have #47 jets and 3.5 power valves. Be aware the power valves in the new rebuild kits DO NOT fit corectly in the 94 body. Reference the attached picture. the left plug is machined for the 94. The PV on the right is what comes in the kit. I also recommend not using the fiber gasket that comes in the kits. Replace it with a nylon gasket sized to the modified PV.

    Attached Files:

  24. arto
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    Location:
    Calgary, AB

    arto Member

    Can you get Strombergs with the correct vacuum hookup for a stock 8BA distributor?
  25. Splinter
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    Los Angeles, CA

    Splinter Member

    Don't know if it works the same, but I've been told the way to check for a blown PV on a Holley is to run the idle screws all the way in...if it continues to idle, you've got a blown power valve. I'd check your fuel pump- might be hinkey in the check valves and start flooding your carb with high fuel pressure as the engine revs build, overpowering the floats and flooding it out.
  26. six pack to go
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    new jersey

    six pack to go Member

    Updates?? Im in the same boat with my 2x2 setup....
  27. junk yard kid
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    san diego,CA

    junk yard kid Member

    Mine did the same thing, the clip fell of the back of the accerator pump rod and slid out enough where it didnt work, pushed it in and it fixed it.

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