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Magneto question

Discussion in 'The Hokey Ass Message Board' started by vrod64, Apr 6, 2012.

  1. Running a Vintage Joe Hunt magneto on a SBC. The mag was rebuilt in 1974 by Hunt, put in a box and pulled out in December. 37 years later.

    Motor starts up perfect, runs great at slow acceleration, but if I gas it off the line, it boggs till around 2500-3000 rpm then like a switch......motor comes alive.

    Could the magnet be weak ? Does shelf life weaken the polarity in the mag ?

    Was told that is probably the problem.

    Thanks

    V
     
  2. shinysideup
    Joined: Sep 1, 2008
    Posts: 1,627

    shinysideup
    BANNED
    from ruskin, fl

    Check your timing. Seems you have no advance.
     
  3. brigrat
    Joined: Nov 9, 2007
    Posts: 5,380

    brigrat
    Member
    from Wa.St.

    Sounds more like a timing, timing advance problem.
    Mark your deg. on the harmonic, put a timing light on it to see what your timing and advance, if any, are doing.
     
  4. Thanks guys. The Mag was set up with a 28 degree advance. Does that help ?
     

  5. shinysideup
    Joined: Sep 1, 2008
    Posts: 1,627

    shinysideup
    BANNED
    from ruskin, fl

    When does full advance hit and what is that #?
     
  6. I am running a 327 with 4 - 48 IDA Weber carbs.......lots of fuel. Custom ground cam to facilitate the webers.
     
  7. brigrat
    Joined: Nov 9, 2007
    Posts: 5,380

    brigrat
    Member
    from Wa.St.

    Spec. card may say it's 28 Deg. but after sitting on the shelf for 30+ years is it really?
    You need to know at RPM it is all in at.
    Hopefully your running a manual trans with stiff gears, an auto with high gears would bog off the line as well.
     
  8. shinysideup
    Joined: Sep 1, 2008
    Posts: 1,627

    shinysideup
    BANNED
    from ruskin, fl

    Is there an echo in here?
     
  9. Yeah, pretty sure it is 28 degrees, it was in a tomb (box) with all the original paters and the adv card was attached to the side post. Pulling it and having it checked next week. Thought the age and weak magnet inside was hopefully the cause.
     
  10. What initial advance did you set it at? Are you sure it doesn't have the advance locked? My vertex is setup like that. In competition you don't care about advance, you just set the timing where you want it.
     
  11. oj
    Joined: Jul 27, 2008
    Posts: 6,257

    oj
    Member

    Did the motor accelerate strong before the magneto?
    If weak magnets etc then it wouldn't work right at all.
    If you have never seen the advance mechanism down under the base oit is an absolute marvel, there are a number of brass plates that are likely hand filled in shapes to create the advance. The plates are stacked and i recall 4-5 of them, they have some kind of lubricant on them so they can moved to create the advance, i bet the oil has 'set up' on your advance plates. You can take the thing apart, seperate the generator from the shaft, and the advance is located just above the tach drive. Post pics of it when you get it apart, it really is something to see.
     
  12. Thanks Kerry and OJ.

    It was a fresh moror I built over Christamas with some good parts. Threw the mag on for grins, ran it at some Nostalgic drags last month and once above 2500 rpm, It pulls super strong.

    The grease knob on the side was packed with "fresh" 37 year old grease,

    I will know more next week when I have it checked.
     
  13. lippy
    Joined: Sep 27, 2006
    Posts: 5,556

    lippy
    Member
    from Ks

    Plug gap also .018 or so?
     
  14. DaveyJonez
    Joined: Feb 20, 2006
    Posts: 423

    DaveyJonez
    ALLIANCE MEMBER
    from Houston

    And solid core wires, Non Resistor Plugs?
     
  15. Heo2
    Joined: Aug 9, 2011
    Posts: 661

    Heo2
    Member

    Webers act like this when they not calibrated right
    in the trasition from idle to midrange
    so long time since i worked with them now
    so i dont remember the cure and there is
    a lot of tuning options on them
    I newer had a weak magneto but compleatly dead ones
    after not being used for a long time
    the cure is to short them (ignition of) and spin them
    and you remagnetisise (if thats a word) them
     
  16. lippy
    Joined: Sep 27, 2006
    Posts: 5,556

    lippy
    Member
    from Ks

    I'm going with Heo2 on this one. Carbs. Lippy
     
  17. Gap .02, Solid core wires yep, Carbs are synced well, but that may be part of problem. I rebuilt them also. I believe since they are 48 IDAs (4 of them)on a lil 327 is part of my bog.

    But the imulsion tubes and gets are within spec of what the motor needs.

    Thanks. Happy Easter
     
  18. For the record.....i pulled the mag and it had a weak coil. So at low rpms it was not hitting on all 8. Too much fuel until the revs came up and it started to make spark. Motor now runs the way i built it to run.

    Thanks for all the input
     

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