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F4 YF Backfiring through carb

Discussion in 'Early CJ5 and CJ6 Tech' started by Howard Eisenhauer, May 25, 2014.

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  1. WorkInProgress

    WorkInProgress Member

    Sounds like something I bought at local boat dealer called Powertune I think by Mercury
     
    WorkInProgress, May 31, 2014
    #21
  2. Alan28

    Alan28 Well-Known Member 2022 Sponsor

    I don't really understand and I have a F4 Hurricane which works well. At least.
    I cannot give an advice too, sorry but I know that you are a good specialist so you'll find the solution.The explosion comes back from the engine, so the valve is open at a wrong moment.

    I had a good result with my engine when I turned the "delco" to the right, it is the timing if I understand well.
    I cleaned the filters of the carburetor before, the one for the accelerator pump was quite obstructed.

    Maybe just changing the timing is enough. It takes time to check but easy to do.

    It happend when an engine was very hot, on old cars. Maybe changing the quality of spark plugs, there was "hot spark plugs and others, I don't know all models but maybe it is good to check the spark plugs.

    By the way I had one broken a little bit so it was wrong and with the new one engine is perfect.

    I cannot help you and sorry for this, this engine is quite perfect, just change what is wrong, you are a specialist, maybe you have an electricity leak somewhere in high voltage, check also the wires... Soon it will be good!
     
    Alan28, May 31, 2014
    #22
  3. Ggg

    Ggg Member

    It is leaning out in the accelerator circuit. Once up to speed it stops backfiring so just under rpm transition. Try choking it a bit to fatten it up and see it that helps. If it does then it definitely a lean accelerator circuit condition in the carb.
     
    Last edited: May 31, 2014
    Ggg, May 31, 2014
    #23
  4. Mike S

    Mike S Sponsor

    I agree that it is most likely leaning out in transition ----------- BUT, that alone will not ignite the fuel/air mixture in the manifold.
     
    Mike S, May 31, 2014
    #24
  5. Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    I'm back at it tomorrow- first off on my to-do list is a leakdown test, then vacuum test, then if necessary re-check valve lash then try the water trick & if none of that shows any issues a different distributor/cap.

    H.
     
    Howard Eisenhauer, May 31, 2014
    #25
  6. PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    "It is leaning out in the accelerator circuit. Once up to speed it stops backfiring so just under rpm transition."
    I would tend to think the same... but also I've had that condition with ignition troubles, such as dirty points or bad timing.

    I would suggest doing the easy stuff first, like the vacuum check... or retarding the timing a couple of degrees, just to see if that helps.
     
    PeteL, May 31, 2014
    #26
  7. Glenn

    Glenn Kinda grumpy old man Staff Member

    I don't consider that backfire, I don't hear a distinct explosion. You might be onto something with the carbon suspicion. Idle screw closed should kill the engine. Does it act that way when the engine is cold? Carbon would have to get hot first, I would think it would at least do it less. How about idle screw closing on a cold engine. Could see if that makes a difference also. Compression readings indicate valves are closed when they need to be, but I have had to readjust an exhaust valve before because I got the clearance too close and I realized it when it got hot.
     
    Last edited: May 31, 2014
    Glenn, May 31, 2014
    #27
  8. Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    :mad:


    OK, why didn't one of you so-called geniusesusses tell me the $%^*! distributor *spins* in the other $%^*! direction !!!

    Problem solved.

    Please return to your regularly scheduled posts.

    H.

    p.s.- :mad:
     
    Howard Eisenhauer, Jun 1, 2014
    #28
    FinoCJ and Vanguard like this.
  9. Glenn

    Glenn Kinda grumpy old man Staff Member

    :rofl: With the way it sounded I wouldn't have thought plug wires would be the issue. ;)
     
    Glenn, Jun 1, 2014
    #29
  10. Mike S

    Mike S Sponsor

    But Howard, I did tell you that about 15 posts ago..........just a slightly different terminology.

     
    Mike S, Jun 1, 2014
    #30
  11. PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    New at this, Howard?

    R)
     
    PeteL, Jun 1, 2014
    #31
  12. Ggg

    Ggg Member

    Well now I feel a little better about misreading the spark plug gap and setting my plugs to the point gap specs.
     
    Ggg, Jun 1, 2014
    #32
  13. Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    I would not have thought it would run that well firing 1-2-4-3 vise 1-3-4-2! Info shows some V-W's did rotate clockwise with 1-2-4-3 but that's not an F-head. Glad you didn't tear down your new engine though.
     
    Walt Couch, Jun 2, 2014
    #33
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