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Teach me about timing, mallory dist. issues

Discussion in 'The Hokey Ass Message Board' started by 54BOMB, Apr 9, 2007.

  1. 54BOMB
    Joined: Oct 23, 2004
    Posts: 2,101

    54BOMB
    Member

    64 ford 390, new Mallory Unilite Vacuum advance distributor. I found the timing mark, and also checked TDC and they matched up. Set the timing at 6* as per a service manual and then hooked up the vacuum line, the timing went to 30* at idle and when I reved it up it was showing 52*. I thought well thats a little high. I called mallory tech line and they said its impossible to have more than 45* ( 360 degrees / 8 cyl = 45* ) and that the distributor is only designed to have 24* advancement. "you have a bad timing light, set it by ear so it doesnt buck against the starter and set it so it accelerates ok" I did want to check it against another timing light but I didnt feel comfortable just doing it by "ear". Got another timing light and it has the same readings. One thing to note it made no difference in driving with the vacuum advance hooked up or not hooked up,and I checked with edelbrock and the correct vacuum port. What am I missing? I am going to order the advancement kit and see if that fixes it.
    Thanks for the help
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 46,102

    squirrel
    Member

    45 max at the distributor, 90 degrees max at the crank

    that's kind of typical for full vacuum advance....if the car runs ok then leave it alone. you might try connecting the advance to a full time vacuum port on the carb instead of the ported one.
     
  3. 54BOMB
    Joined: Oct 23, 2004
    Posts: 2,101

    54BOMB
    Member

    When I looked at the edelbrock website they mentioned a "timed" vac port and full vacuum port. The timed vac port has no change at idle and back up to 50 at higher rev's. Like I said it runs rine either way, I just didnt want an overly lean condition. Thanks Squirrel
     
  4. 53sled
    Joined: Jul 5, 2005
    Posts: 5,819

    53sled
    Member
    from KCMO

    lean refers to air/ fuel ratio, not timing. I have timed a few by ear, (i've also crossed the wires at the cap:D) but a good timing light IS the best way.
     
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  5. 54BOMB
    Joined: Oct 23, 2004
    Posts: 2,101

    54BOMB
    Member

    I thought that if you had to much advance it could cause it to run lean. I like using a timing light too esp since I own one.
     
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 46,102

    squirrel
    Member

    nope, the only way you can get it to run lean is by not having the carb set up right, or having a vacuum leak. Timing is timing, mixture is mixture, they are independent...although they can both make the engine run bad if they're wrong.
     
  7. DrJ
    Joined: Mar 3, 2001
    Posts: 9,422

    DrJ
    Member

    More bluntly;

    You should definitely hook it up to the full time vacuum port (The port on the driver's side of the carburetor) if this is a street driven car.

    52º is fine as long as it retards under load, as manifold vacuum is designed to do and does under load.

    For some reason Edelbrock "recommends" only timed vacuum, which is fine for a dyno tuned for full power at a specific RPM drag race only car that is used wide open or off most of it's life but it's not the best for driving in traffic throttle response across the throttle range or for mileage.
     
  8. 54BOMB
    Joined: Oct 23, 2004
    Posts: 2,101

    54BOMB
    Member

    Why do people say " your going to burn a hole in your piston" if your timing is too advanced? Is that more from detonation, the piston and the spark running into each other if the spark is too early?


    Dr.j - it is a daily driven car and the thats the reason I went with a vac advance style distributor. I am using the full port on the drivers side not the timed port. Made more sense to use the full time vacuum if you got a vacuum dist.
     
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 46,102

    squirrel
    Member

    Timing and mixture are independent, but both can contribute to detonation, which is what burns that hole in the piston. It's not that the piston and spark run into each other...the fuel/air spontaneously combusts because the heat/pressure is too high, instead of burning as it normally does.
     
  10. 54BOMB
    Joined: Oct 23, 2004
    Posts: 2,101

    54BOMB
    Member

    I understand detonation , like in a diesel and a lawn mower, I didnt phrase my question well. But I understand what your saying. Im just going to run it, Im already planning on a fresh engine anyway, I was just trying to understand the mechanics behind how stuff works. thanks for the help
     
  11. Lobucrod
    Joined: Mar 22, 2006
    Posts: 4,118

    Lobucrod
    Alliance Vendor
    from Texas

    Having the vacuum advance hooked up to full manifold vacuum will help fuel economy and idle quality (that is if you dont have a wild cam that has little vacuum at idle). Does nothing for performance. When your foots in it there is no manifold vacuum and you only have the mechanical advance. Total advance (initial + mechanical + vacuum) of 52 is not out of range. I normally set the total advance with the vacuum unhooked at somewhere between 32 and 38 depending on the motor then hook up the vacuum and let it ride. If you get some kicking back when starting then back it off a few degrees.
     
  12. 54BOMB
    Joined: Oct 23, 2004
    Posts: 2,101

    54BOMB
    Member

    Ive noticed if the timing it too advanced it sounds horrible when starting and it cranks and cranks. Right about 8*( with out vacuum) it fires up quick and sounds normal. The only drivabilty issue is a real slight surge if im at a constant speed for a while but thats there no matter what timing im at, I think thats associated with the 125k on the engine. Plugs look tan around the ground and electrode.
     

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