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Fhead Tuning Issues

Discussion in 'Flat Fender Tech' started by pfmg, May 27, 2018.

  1. May 27, 2018
    pfmg

    pfmg Member

    Billerica Mass
    Joined:
    Feb 10, 2010
    Messages:
    258
    i have been messing with this fhead for a while now, it runs ok i guess. But still seems a little rough, and i cant get a real good reading with the vacuum gauge, it fluctuates around 15-16, i have always used the vacuum gauge as a indication of how good the engine is running.

    In the past i swapped out the points to petronix ignition, and had Rick rebuild me a fresh carb, been playing with it like this since last year. Spent a lot of time messing with the timing too,

    The background on the engine is it was rebuilt by these guys right before i got it.
    Engines - MDR Engines

    Today i started to do a little more digging, i did a compression test, and cylinder leak test.

    Below are the results, and pics of the plugs. Plugs look good, comp looks good, and leak down reading are within speck, but there something odd when doing the leak down test.

    On cyl, 1, 3 and 4 as i turn up the leak down pressure, the leak gauge rises steadily with the input pressure gauge, it lags slightly behind until i hit the test pressure, which was 100psi, then it settles in at its resting pressure, indicated by the leak % on the chart. They look good

    On Cyl 2, ( also the cyl with the highest leak reading). The pressure lags way behind, even gets stuck for a better word then pops up to the resting pressure. Almost like something leaks until some pressure is built up to seal it.

    The only place any leakage is showing up is in the dipstick, which would indicate rings i think, but compression is fine


    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
  2. May 28, 2018
    william_cj3b

    william_cj3b 3BOB driver

    Milton, FL
    Joined:
    Nov 17, 2003
    Messages:
    421
    Is your timing stable? If not look at the distributor bushings and the advance mechanism.

    You're not detecting any leakage in the intake or exhaust? Even while the leak down gauge is lagging behind (before it "pops up") in #2?
     
    Last edited: May 28, 2018
  3. May 28, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
    Joined:
    Sep 21, 2002
    Messages:
    12,367
    How many miles are on the engine? How many miles on the plugs?
     
  4. May 28, 2018
    pfmg

    pfmg Member

    Billerica Mass
    Joined:
    Feb 10, 2010
    Messages:
    258
    I adjusted the valves, timing, And carb, found a vacuum leak, it’s running pretty good now, still can’t get better vacuum. Going to run some mystery oil through the fuel and oil, think it just might be gummed up a bit

    The engin has about 1500 miles since rebuild. It pretty much has sat for the lasted couple years.
     
  5. May 28, 2018
    pfmg

    pfmg Member

    Billerica Mass
    Joined:
    Feb 10, 2010
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    258
    Put new plugs in today too
     
  6. May 29, 2018
    PeteL

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

    Hills of NH
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    Aug 3, 2003
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    9,754
    Looks a tad rich on the plugs, but I'd be very happy to have your readings. Is there really a problem?
     
  7. May 29, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
    Joined:
    Sep 21, 2002
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    X2!
     
  8. May 29, 2018
    pfmg

    pfmg Member

    Billerica Mass
    Joined:
    Feb 10, 2010
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    258
    the reading are good, the inital problem was it just was not running right, could have been any of ten reasons. i did what i usually do in this case, and hook up a vacuum gauge, the readings were bad, not only low, but fluctuating bad, bouncing from 14-17. So i started the work last year, fresh carb rebuild from ScoutPilot, petronix inginion, and some tuning. It got better, just not great. i hopped back on it now and i figured id do the compression and leak-down test just to see if the engine was fresh like i was told, and i agree, the reading look good, so i went back to the basics this weekend, replaced the plugs, adjusted the valves, timing and carb again and found a vacuum leak and fixed it. its running pretty good now, better than it has vacuum reading are still lower than i like, dont really know what the cause of that is. This CJ sat for a long time, so im going to put some miles on it and see how it goes
     
  9. May 29, 2018
    PeteL

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

    Hills of NH
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    Restricted exhaust? I once had squirrels completely pack my exhaust system with acorns.
     
  10. May 29, 2018
    pfmg

    pfmg Member

    Billerica Mass
    Joined:
    Feb 10, 2010
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    interesting, have not looked at exhaust, i could just disconnect at the manifold to rule that out, thats easy
     
  11. May 29, 2018
    PeteL

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

    Hills of NH
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    I suppose.
    But my wise old Dad always told me about old vehicles, "if it ain't broke, don't fix it."
     
  12. Jun 1, 2018
    pfmg

    pfmg Member

    Billerica Mass
    Joined:
    Feb 10, 2010
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    Still no luck, I have rechecked the compression, because the first time I did it, it was kind of quick with an beat up gauge.

    New readings are even better

    Warm engine. Dry test
    1 - 130
    2 - 135
    3 - 135
    4 - 130

    It’s still too rich. If I lean it out it runs terrible, almost not at all. If I adjust timing to a place where it will run the leaner setting, it runs terrible. Rough missing etc.

    Back where it runs pretty good, is a almost acceptable, but I know it’s not right. Vacuum is only at 15, and it’s fouling the plugs
     
  13. Jun 1, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Does it stumble or hesitate on acceleration? You say it has been sitting mostly for 2 years, most likely the carb is somehow gummed up inside. Try some seafoam?
     
  14. Jun 1, 2018
    pfmg

    pfmg Member

    Billerica Mass
    Joined:
    Feb 10, 2010
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    258
    no, pulls pretty good and runs overall pretty good now, just bad Vac reading, and seems a little rich
    Was sitting before i got it, since then i:
    replaces solex carb with fresh carter from Rick,
    new points, cond, then tried petronix, and new wires
    adjusted valves,
     
  15. Jun 1, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
    Joined:
    Sep 21, 2002
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    How about the carb base gasket? Any chance it's leaking? Did you check it for fit on the base of the carb? I'm going to assume it has the notch for the vacuum hole in the base....I imagine it wouldn't idle worth a darn if it didn't have it.

    Also wondering if the fuel pump pressure is too great? Maybe overcoming the needle valve just enough to cause it to run rich?
     
  16. Jun 1, 2018
    PeteL

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

    Hills of NH
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    Sure your vacuum gauge is accurate?

    If so, the symptoms could be restricted exhaust.
     
  17. Jun 1, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Yeah, he didn't indicate if he checked that as you had suggested.
     
  18. Jun 1, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Also, we're assuming the timing is correct.
     
  19. Jun 1, 2018
    Greevesman

    Greevesman Member

    Napa, Ca
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    Oct 12, 2014
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    I vote for fuel pump excess pressure.
     
  20. Jun 1, 2018
    PeteL

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

    Hills of NH
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    On a Carter YF flooding usually would show up as leakage from under the bowl.

    As for timing - set it and forget it. It is a specification, not an adjustment.
     
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