shovel head

Discussion in 'Classic Models' started by redneckrob, Mar 18, 2012.

  1. redneckrob

    redneckrob New Member

    I have questions but no answers. It's sunday and beautiful out side my 74 shovel is down now for two weeks. I put a new top end on it, rebuilt the carb, new coil,plugs,and wires. When I can get it started it runs good till it warms up then it pops and backfires. It has a crane cam hi-4 ignition in it. This is my second coil in it and now it seems that this coil has gone bad. What can I do and what could be the problem with the coils.
  2. SledDog

    SledDog Senior Member Staff Member Moderator

    Welcome to the Forum. Perhaps more info will help us solve it. Have you timed the motor? Is the pop and backfire at idle, at speed under load or deceleration?

    I have a link to the what I think is the correct manual for your ignition. It call for installing a VOES switch. Have you done that? The link also gives the info on how to static time the system, along with other setup info. What procedure did you use to determine the coil was bad? Can you post this info? It will help us with assiting you in troubleshooting the issue.

    But I did find this in the installation and troubleshooting info:

    Field experience has shown that popping back
    through the carburetor, misfiring, and intermittent failure
    (especially after the engine gets hot) are usually
    not caused by electrical problems within the HI-4.
    Carburetor problems, fouled spark plugs, coil failure,
    and loose wire harness connections are the most common culprits.

    crane cam hi-4 ignition pdf
    Last edited: Mar 18, 2012
  3. Jack Klarich

    Jack Klarich Guest

    Are you sure it is the coil and not the pick up? Check the pdf Sleddog provided I think it gives you diagnostics.
  4. poohbear

    poohbear Active Member

    You may also check the wires for shorts, if you are using the choke and once it released something may be shorting out.
  5. redneckrob

    redneckrob New Member

    Timming is set at tdc. Starts up and throttles up good when cold. When warm at half throttle or under load backfireing starts. Have been running hi-4 for a couple of years with a dual fire coil. Changed coil after I tried to run oem points and had no fire.Went back to the hi-4 with new coil and ran good till hot same problem. Tried points again and no luck.Have 12v on the negative side of both coils when power is aplied to positive side.
    Running a s&s supper B carb, new wires on the hole bike, with new plugs and wires.
  6. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

    In the past there have been problems with ignition modules breaking down when hot easy way to diagnose is to get bike to the point where it starts to give problems then open the points cover and spray the ignition module with canned air / spray duster as it comes out cold it will cool the ignition module if bike then runs ok you have found the problem area

  7. R_W_B

    R_W_B Senior Member

    Wow that PDF is one interesting blast from the past Sleddog. It almost sounds like he has his VOES set to the "race only" instead of the "ALL OE POINTS" advance curve. Thereby causing pre-ignition and overheating and resulting carbon backfire.
  8. redneckrob

    redneckrob New Member

    The hi-4 is set on the same settings. The only thing that was changed was the jugs, pistons & rings, heads, rockerbox. The problem started a little less than an hour of run time. I was told that it was the coil so I changed it and still have the same problem with the new coil. It wont even try to run with point. I have seen the crane cam page with the settings and all is set to run.
  9. JollyRoger

    JollyRoger Member

    Hi, Just want to check if you found the problem. I have a 1981 that started with the same problem after I installed a Hi-4. She starts first time, idels perfect, goes like a freight train... Then boom sputters and lost of power until she has cooled down.