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Anyone know how to...

Discussion in 'Pacific Region' started by Topdown, Sep 30, 2003.

  1. Topdown

    Topdown 1/2 ton status

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    Anyone know how to adjust the curve on a distributor? I have a butt-load of low rpm ping thats driving me nuts.

    Thanks
     
  2. ntaj*ep

    ntaj*ep 1/2 ton status

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    Well ya........ /forums/images/graemlins/rotfl.gif
    Are you sure that you have the vac. advance hooked up right? If its adjustable is it adjusted right?
    Setting up your "curve" or mechanical advance is cake, it just takes trial and error. What type of dist. do you have?
    There ary funky looking weights inside your ignition cap under the ignition rotor. Theres springs that hold the weights in. The differential between the weights and the strength of springs "sets" the advance curve /forums/images/graemlins/thumb.gif........
    RU with me, if I lost ya let me know. /forums/images/graemlins/thumb.gif
     
  3. Topdown

    Topdown 1/2 ton status

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    yes its got vac advance, no its not adjustable, yes its set up right.

    Yes I know the weights and springs you are referring to and no you havent lost me yet.

    Is there a guideline to follow that will help establish a good baseline to start from?
     
  4. kennyw

    kennyw N9PHW Premium Member

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    There are a couple things to check in addition to your timing curve. Older GM 350's are good for blowing head gaskets like my '79 has done recently. Mine is getting alot of pinging under high RPM highway driving though.

    Also check to be sure your timing mark is acurate. Rotate the engine to TDC on the compression stroke (take spark plug out and put thumb over hole to create wistling sound). When wistling stops your timing marks should be close to 0 deg.
     
  5. Goober

    Goober 1/2 ton status

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    I'm assuming you have the good old GM HEI, correct? If you have an old Delco-Remy points type distributor then I would recommend pulling it out and picking up an HEI from someone that has a spare they want to get rid of. You could also pick up a new Accel HEI unit for less than $150. The Delco-Remy distributors are not bad distributors but they require a lot more attention then an HEI and it's getting harder and harder to find a good set of points these days.


    Did it just start pinging recently? Has anything in the motor been changed?


    Before going through all that trouble, make sure you check the easy stuff. Take a look at the plugs:

    [​IMG]

    Make sure you have the correct heat range. If your plugs are too hot, the electrodes will wear prematurely and pre-ignition could occur. If they are too cold the electrodes will get covered in carbon, oil and gunk (a technical term /forums/images/graemlins/grin.gif) buildup on them causing the spark to jump to ground instead of arcing across the electrodes.

    Get out your timing light and set your initial advance. If you have a stock engine then just stay with the stock settings. If you have an engine that has been modified then there are no "perfect" settings that you can look up since it will vary from engine to engine. Initial advance can vary from 6 degrees btdc to as much as 18 degrees btdc depending on how the engine is put together. If you don't know what it should be then a nice safe setting of about 6-8 degrees btdc should be safe.

    Next open up the distributor and check the pivot pins that the advance weights spin on. There should be some little nylon bushings that sit in the holes and stop metal to metal contact. These little buggers wear out ove the years and cause some pretty erratic timing. They are cheap and easy to replace (sorry, I don't have a part number .... check with NAPA).

    If you want to go farther than that, you will need to go buy some new advance springs. You could just get one of the Crane adjustable advance kits (about $20) that will come with the vacuum can, springs, a lockout tab and pretty simple instructions on how to adjust it. I think it's a pretty good kit but you gotta be careful once you start changing stuff around and make sure everything else is 100% or you will spend all your time chasing gremlins.

    You CAN change the curve by shaving the edges of your advance weights but that is usually not necessary and it can really be a pain in the butt. It's much easier to change the advance rate by changing the springs on your advance weights. You can make some pretty serious adjustments with different weights.



    Here are a few links:

    HEI Tuning Secrets - Damon Nickles has a good writeup on adjusting HEI ignitions. Keep in mind that he is working on lighter, higher RPM (usually) engines for a car. Same tricks apply with a heavier truck but you may want to experiment a little. Good tips and a good reference.

    Some HEI pics from a 'vette forum.


    Have fun!
     
  6. ntaj*ep

    ntaj*ep 1/2 ton status

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    Just takes trial and error bro.......
    If you want advance later heavier springs will be needed, sooner lighter, ect.
    If you think your just flat out getting too much total advance, then you have another issue altogether. /forums/images/graemlins/eek.gif
     
  7. BurbinOR

    BurbinOR 3/4 ton status

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    In addition to the great advice given, make sure you have NO vac leaks at all /forums/images/graemlins/laugh.gif.

    You can also put an adjustable vacuum advance on the HEI........did it on my 79 before I went to TPI. Was worth doing.
     

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