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Technical Flathead problems fuel/ign questions

Discussion in 'The Hokey Ass Message Board' started by reverb2000, Mar 22, 2014.

  1. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    reverb2000
    Member
    from Houston TX

    Yes I have searched and no one asks direct questions so hard to decipher a answer.
    49 Ford flathead, 80lbs compression plus or minus 15 %, new hei dist, new holley 94, stock internals, stock fuel pump.
    A month ago the engine ran great, then started running rich. That propted my to change the dist/ wires/plugs (which I wanted to for a while), and the carb which I had no history on...it came with the car.
    Engine starts only with full choke and of course runs rich. I checked all cyl while running with a heat gun and all are firing and heating up evenly.
    I have changed the plugs, and checked for vacuum leaks. In the upper RPMs one side of the engine the exhaust sound changes to a blap blap blap tone. Almost like a misfire, but I have checked the plug wires at least 20 times now.
    The car cannot be driven, and instead of asking a million questions I see I have two issues.
    1) There is air in the glass fuel bowl. I have checked for vacuum leaks on the suctions side and have found none. I know there is a ck valve in the stock diaphragm pump and its either pushing or pulling. Other than a air supply between the pump and fuel, is there any other reason a pump would have air in it...seems to be at the upper RPMs. The engine runs, but very rich and will not get into the upper rpms due to what sounds like misfire or a fuel supply issue.
    2) Also the carb. Its a new single holley 94. haven't checked the jet size or power valve size. Screw in the mixture screws and nothing happens. If anything it runs better. I understand the carb and vacuum/idle circuits, but do not want to disassemble it until I can rule everything else out. If the power valve is too small, I am guessing it will open at idle?
    Im sure I have left something out, but I am attempting to be clear and concise.
     
  2. GMC BUBBA
    Joined: Jun 15, 2006
    Posts: 3,350

    GMC BUBBA
    Member

    mY VOTE IS FOR A CARB PROBLEM....
     
  3. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    reverb2000
    Member
    from Houston TX

    ok thanks...small powervalve? When I say a new carb, I mean I just put it on yesterday and the company is closed today so I cant get the specs. The air horn was slightly larger than my stock 94 so wondering if that is just a manufacturing change to get around copyrights or if its for a different application.
    Isn't air in the glass fuel bowl when I attempt to get into the upper rpms a issue also? I am thinking the issue is two fold. I am having to move to another house, otherwise I would just keep troubleshooting myself.
     

  4. 2) Also the carb. Its a new single holley 94. haven't checked the jet size or power valve size. Screw in the mixture screws and nothing happens. If anything it runs better. I understand the carb and vacuum/idle circuits, but do not want to disassemble it until I can rule everything else out. If the power valve is too small, I am guessing it will open at idle?


    The bolded text is a big clue that you have a carb issue.
     
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  5. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    reverb2000
    Member
    from Houston TX

    I think the carb also...funny thing is I put the old carb on and it did the same thing...but is the vacuum opening the power valve, and bypassing the idle circuit? I want to have a second guess before I open a new carburetor.
     
  6. R Pope
    Joined: Jan 23, 2006
    Posts: 3,310

    R Pope
    Member

    Could be broken valve springs or sticking valves, I had a flattie that wouldn't rev over 1500 RPM, two intake springs were broken.
     
  7. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    reverb2000
    Member
    from Houston TX

    Thanks pope...I was thinking that also so I used a heat gun to check temps and they were heating evenly on all cyl. Did it run super rich and make a popping noise thru the exhaust at the upper RPMs?
    Wouldn't a broken valve spring show up in a compression test? How would a valve physically stick closed?
    The engine doesn't idle like it did either. Seems to labor quite a bit and wants to die.
     
  8. blowby
    Joined: Dec 27, 2012
    Posts: 6,104

    blowby
    Member
    from Nicasio Ca


    I ran my flattie through the gears day before yesterday full throttle, after which it barely limped home. After tearing the carb apart twice I pulled the plugs. Valves had floated and knocked the plug gaps down (to zero in some cases). Luckily none broke.
     
  9. A month ago the engine ran great, then started running rich.



    So what happened?
    Did you do anything ? No matter how trivial you think it might be
    Did it just fall out of tune ?
     
  10. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    reverb2000
    Member
    from Houston TX

    Nothing traumatic happened....well, 6 months ago the throttle caught in the open position and the engine revved a bit high but shut it down and ran fine since.
    Seems the underlying issue is the mixture screws not affecting the idle circuit...I see timing can affect it also, but being a new carb and still not sure of the specs till Monday.
     
  11. Worth a try :
    Take the mixture screws out,
    Fashion a small rubber hose onto a blow gun, like vacuum line or windshield washer hose.
    Place a rag over the carb just incase , to catch any fuel coming out .and keep junk from getting in
    Turn your air pressure down to about 50 psi,
    Hold the hose into/onto/over the hole where the mixture screws go.
    Hit the trigger and clear that passage.

    Reinstall your screws and give it try tuning them in.
     
  12. King ford
    Joined: Mar 18, 2013
    Posts: 1,261

    King ford
    ALLIANCE MEMBER
    from 08302

    You may have a collapsed muffler restricting the exhaust ,when this happens the vacuum goes down and the carb won't respond properly ....take the mufflers off .....also I have seen ford cars from the 70s with double wall crossover pipes collaps and cause this!
     
  13. Restricted exhaust can be diagnosed in 30 seconds.
    Hook up vacuum gauge , blip throttle and the needle will drop to zero if the exhaust is restricted
     
  14. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    reverb2000
    Member
    from Houston TX

    running straight pipes...currently disconnected about a foot past the exhaust headers. I am going to blow thru the mixture screws in a second.
     
  15. silversink
    Joined: May 3, 2008
    Posts: 912

    silversink
    Member

    when you put the screws back in turn them 1 1/2 turns out to start----not sure if you knew that
     
  16. Ulu
    Joined: Feb 26, 2014
    Posts: 1,730

    Ulu
    Member
    from CenCal

    Sounds like two issues at once. Maybe gas tank not venting, plus a vacuum leak?
    But that doesn't explain the richness that started before the carb swap.

    How does the vacuum gauge act as you run the engine up and down?
     
  17. R Pope
    Joined: Jan 23, 2006
    Posts: 3,310

    R Pope
    Member

    A broken spring can exert enough pressure so the low speed vacuum will stay up, and the compression too. That won't explain the rich mixture, though. Two problems?
     
  18. Did you backfire at all ?
    Pay special attention to the power valve discussion and how the amount of manifold vacuum effects them.

    http://www.popularhotrodding.com/enginemasters/articles/hardcore/0510em_carb/
     
  19. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    reverb2000
    Member
    from Houston TX

    Yes I know about the power valve. No it didn't backfire. The tank is venting. There are no leaks. I pressurized the tank w air with soapy water on all connections.
    HEI dist. vacuum port plugged.
    With the rpms up I can turn the mixture screws and in any position other than 100% closed, it loads the engine and bogs....not a lot, but enough to hear.
    I blew thru the mixture holes and its a clear shot.
    Vacuum is at 17in and holds until starts to backfire, then falls 14 and holds....when I mean backfire I mean a rythmatic bap bap bap...I am leaning to valve issue, but cant check today...packing and getting ready to move, and cant find the valve covers anyway:)
    If anyone has another idea that I can check fairly quickly I appreciate any input.
     
    Last edited: Mar 22, 2014
  20. Mixture screws are for idle adjustment only . If the throttle plates are open (as you say rpms up) they do very very little.

    If you had bad valves the vacuum gauge would not be steady.
     
  21. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    reverb2000
    Member
    from Houston TX

    Thanks for the ideas everyone...I am going to call the company I bought the carb from on Monday and ask for the specs and the ok to disassemble it.
     
  22. tubman
    Joined: May 16, 2007
    Posts: 4,459

    tubman
    ALLIANCE MEMBER

    Take the carb off the car, take the top off the carb, set it on a bunch of folded up paper towels on a chunk of 2X4 and fill the float bowl with gas. This will tell you if you have a leaking power valve, if you don't believe in the idle screw method.

    With all the varieties of PV's and gaskets these days, I always do this to double check the PV any time I change one.
     
  23. George/Maine
    Joined: Jan 6, 2011
    Posts: 949

    George/Maine
    Member

    If it ran good what carb did you have when it was running good.
    When it started to run rich, may only have had a sticking float needle valve.
    Also put the original dist. back on and check to make sure you put wires on correct.
     
  24. In post number 1 he says he has a flatty that he is working on,but in post 19 he says he cannot find the valve covers,,,WTF..exactly What engine do you have????
     
  25. Missed the smiley and the joke there did you ?
     
  26. Ulu
    Joined: Feb 26, 2014
    Posts: 1,730

    Ulu
    Member
    from CenCal

    What a supreme bummer to have your rod acting up on moving day. As if moving itself isn't bad enough. ;(

    2 funky power valves in a row isn't impossible, but I wonder how much crud was in in the float bowl of the previous carb? And the new one now...

    BTW, I have a glass "visiflow" float bowl I use to check the float level on my Holly, but I never ran it except for testing. Too paranoid about the glass & all that heat. Float levels can be tricky to set as the float isn't always square and straight. The glass float bowl does not lie.

    The bap-bap-bap business sounds like a cross-fire rather than a backfire maybe? It's like a classic ignition coil failure symptom as well. Starts up then falls flat under pressure. Puffs out some smoke like it's rich because the spark timing is screwy = incomplete combustion.
     
  27. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    reverb2000
    Member
    from Houston TX

    [​IMG]

    So I checked the pv overnight and no leak...so I wanted to see the value, and nothing on the valve...but I see a brass jet that is extending above the pv...I have never seen this before...any ideas? After looking this picture it appears the numbers are on the pv but its not...that's a reflection..I even looked w my magnifying glass.
     

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  28. ginuine555
    Joined: Jun 17, 2006
    Posts: 104

    ginuine555
    Member
    from louisiana

    I'm with R POPE. If this is the second carb and it is doing the same thing it could very well be a valve problem. Have a flathead that gave similar problem and found a bad valve. Hopefully another carb will do it for you
     
  29. paleot
    Joined: Aug 29, 2011
    Posts: 217

    paleot
    Member
    from louisiana

    One hard backfire could blow the power valve! pull the power valve suck on the diaphragm side if it leaks air through it is bad.
     
  30. reverb2000
    Joined: Apr 17, 2005
    Posts: 440

    reverb2000
    Member
    from Houston TX

    blown power valves will allow gas to leak thru over night...there is no leak.
     

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