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134f Tune Up Issues

Discussion in 'Early CJ5 and CJ6 Tech' started by 60CJ5, Jun 5, 2018.

  1. Jun 5, 2018
    60CJ5

    60CJ5 Member

    Alabama
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    Ok so I have a petronics (sp???) unit under the distributor cap and when I was setting the timing on the jeep as part of a tune up, I noticed that the timing mark jumps around a good bit at idle (maybe 1/4" to a bit more advanced). when I give it gas the timing advances as I would expect but it is still real jumpy.

    This is the original distributor unit.

    Wondering if it is a vacuum issue or just a worn out distributor.

    Thoughts on what to attack first.

    The Jeep is just not running well enough right now for me to take it out. seems ok around the neighborhood but after time it starts wanting to die. I know part of it is a carb issue as I can adjust the idle mixture screw all the way in and out and nothing changes. seems to be running really rich. considering just pulling the Solex carb off and going with the Webber 2bbl and maybe a new distributor (if that is the consensus of the fhead pros here)

    The wife is getting upset that it is not drivable so the budget is opening up :)
     
  2. Jun 5, 2018
    Daryl

    Daryl Sponsor Sponsor

    Bonney Lake, WA
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    I would focus on one thing at a time so you can establish a baseline from where to go. If the carb is obviously a problem then maybe get it rebuilt first. Search ScoutPilot carbs and give him a call to start with. I am not a fan of the Webbers but others have been able to make them work. I have had several of the repop Solex carbs that have actually worked well for cheap.
     
  3. Jun 5, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    Like Daryl said, one thing at a time. I think I mentioned it previously just put a kit in the Solex and there's a good chance that will fix the problem.
     
  4. Jun 5, 2018
    pfmg

    pfmg Member

    Billerica Mass
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    Feb 10, 2010
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    I’m working through a very similar issue
    Fhead Tuning Issues

    Ive done a lot of poking around, but what i just found are some issues with my Petronix installation, we’ll see what changes when i fix those.
     
  5. Jun 6, 2018
    60CJ5

    60CJ5 Member

    Alabama
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    So I started looking at some things and have a couple questions:

    How do I check the vacuum on the Fhead. I have all the original preformed metal tubing. Only rubber tube runs from the T to the vacuum pump.

    I took the distributor cap off and it was a little dusty on the inside but no burn marks. The rotor and shaft is loose feeling. I can move it a good 3-4 degrees. Issue or normal??
     
  6. Jun 6, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    You could disconnect from the vacuum pump and go from the T to a vacuum gauge. If you can noticeably wiggle the shaft from side to side then that's bad. Just a bit of rotation is ok.
     
  7. Jun 6, 2018
    60CJ5

    60CJ5 Member

    Alabama
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    the side to side has a little movement but it does not seem to be excessive. the rotational slop seems to be a lot. if you are looking at a clock (hour hand) if you start at 9:00 it will move to what would be 9:30 to 9:45...

    going to check the vacuum later today.

    I am correct that the fhead does not use vacuum to control spark advance??
    Also, the vacuum line connects to the intake manifold and does not connect to the carb. so how does it affect the carb? (info: I truly do not understand carbs, have the basic idea in that it controls the air and gas mixture, but I really don't understand how it works.)

    the stock PVC unit is just a tube with a smaller tube on a spring on the inside. to be honest in looking at the parts, I have a hard time seeing how it does anything. it looks like air would just flow through it and I have no clue how the spring and inner tube are activated to do much of anything.
     
  8. Jun 6, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    If you don't have a little vacuum module on the distributor then no vacuum advance. Engine vacuum pulls the air/fuel mixture through the carb. so it doesn't necessarily affect it. Being dirty, gummed up, worn out parts, bad accelerator pump is what affects a carb. working right. A Carter YF has a vacuum port in the bottom of the base and vacuum pulls the accelerator pump down at idle. The PCV system allows a metered amount of vapor to be pulled out of the engine so pressure doesn't build in the crankcase. Engine vacuum should pull it to it's metering position (simple terms).
     
  9. Jun 6, 2018
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    :schooled: ON

    Get a glass of water, a plastic straw and a mirror.

    Stick the straw in the water & position the mirror so you can see the straw when you face is down next to it.

    Blow across the top of the straw- in the mirror you'll see the water rise up within the straw- if you blow hard enough the water will reach the top & start blowing out the end.

    In a carb the air flow is controlled by the throttle plate- at rest it's closed. As you push on the accelerator the plate opens allowing the engine to suck more air through the carb. In the carb throat there's a small tube sticking out into the air stream- as the air flows past it gas is sucked up out of the card float bowl through the tube & into the air stream. How much gas comes through is determined by the strength of the airflow and a needle valve that's adjusted by both throttle position and a vacuum signal from the manifold (fancy description for a little rubber diaphragm & a spring) that can restrict how much gas can flow into the tube.

    The throttle throat, tube and needle valve are sized to provide the correct "gas to air mixture" ratio based on the amount of air the engine is capable of sucking, i.e. engine displacement.

    :schooled: OFF
     
    Last edited: Jun 6, 2018
    Daryl likes this.
  10. Jun 6, 2018
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

    Apopka, Fl
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    Good description Howard! :coffee:
     
  11. Jun 6, 2018
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    Were you seriously expecting anything else ?!?




    :D
     
    cookieman, Glenn and Dandy like this.
  12. Jun 6, 2018
    PeteL

    PeteL Member Sponsor 2019 Sponsor

    Hills of NH
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    Are you perhaps referring to the centrifugal advance action?
     
  13. Jun 6, 2018
    PeteL

    PeteL Member Sponsor 2019 Sponsor

    Hills of NH
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    But what about Bernoulli? :confused:
     
  14. Jun 6, 2018
    pfmg

    pfmg Member

    Billerica Mass
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    You mentioned that your timing was jumping around earlier, i had the same issue, the video is in my thread. I also am running the Petronix, and found out i had it wired wrong, i still had the ballast resistor in it, and i might have had the wrong plug wires. I put on some petronix wires, and took the ballast resistor out of the system, and now the timing is dead on, no jumping at all. It’s still not running good, but timing is not jumping
     
  15. Jun 7, 2018
    60CJ5

    60CJ5 Member

    Alabama
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    Was thinking about the carb issue and it all started when I redid the rubber fuel line to get rid of a kink wondering if the kink was holding down fuel pressure??? Picked up a regulator yesterday. Just have to figure out where to mount it. Don't want fuel lines running all over the place but don't see a good mounting spot that is basically in line with stock routing
     
  16. Jun 7, 2018
    Keys5a

    Keys5a Sponsor Sponsor

    Florida Keys
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    Back to the distributor, as Glenn mentioned, the rotor should have little to no side play, but should be able to rotate maybe as much as 1/4" on the outer arc of the rotor. This rotation should be lightly spring-loaded, where it should return to the same position at rest. There are flyweights under the points plate that advance the rotor depending on rpm. These weights have springs that hold them toward center of the shaft, and as rpm increases, allow the spark to advance.
    If these springs are too weak, or missing altogether, your timing will be erratic, with the timing light on the marks bouncing all over the place, at least up to full advance (high rpm) where it may stabilize.
    -Donny
     
  17. Jun 9, 2018
    60CJ5

    60CJ5 Member

    Alabama
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    Just did a vacuum test off the T just down line from the PVC and it is not good 2-3in.... the vacuum lines are 60 years old, are pre-bent new ones available?
    I just adjusted the valves a couple weeks ago and am pretty sure I have them right. only adjusted 2 of the 8 valves and that was just a very little bit. thinking I may have damaged the vacuum lines getting the side valve cover off.

    checked the rotor and it moves but is not "spring loaded" just moves and stays where I move it



    thoughts????

    it is amazing it is running as well as it is.....
     
  18. Jun 9, 2018
    60CJ5

    60CJ5 Member

    Alabama
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    did add a fuel pressure regulator that I still have to adjust but it is 2-5lb and I have it a little off the low side.
     
  19. Jun 9, 2018
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    That's not a valid test point- disconnect the vacuum from the port on the manifold under the carb & plug your gauge into that. 2 to 3" is just not a realistic value.
     
  20. Jun 9, 2018
    Walt Couch

    Walt Couch sidehill Cordele, Ga. Sponsor 2019 Sponsor

    cordele, Ga.
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    And yes it seems your mechanical advance under the breaker plate is not working like it should.
     

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