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Timing question

Discussion in '308/328' started by decardona, Jan 31, 2010.

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  1. decardona

    decardona Formula 3

    Apr 23, 2005
    1,019
    PA
    Full Name:
    Dennis Cardona
    #1 decardona, Jan 31, 2010
    Just installed the dual distributor Pertronix MR 182 kit into my car. When removing the distributors, was very careful to mark them so I could put them back correctly. When I was done the car fired right up, with a bit of backfiring at idle. The car ran rich when on points, so I adjusted the carbs to run less rich. When I got to a point I was happy with, I took the car out for a drive to check. Now it seems to be backfiring in the 4 to 5K rpm range in each gear. So, my question is, is this a carb setting issue, or is it a timing issue? If it is a carb issue, I am sure trial and error will get it right. If it is a timing issue, how do I go about checking it so I can correct it? Thanks in advance for your help.
     
  2. eurogt4

    eurogt4 Karting

    Apr 15, 2006
    243
    Sacramento, CA
    Full Name:
    Mike
    #2 eurogt4, Jan 31, 2010
    Check the relative position of the rotors to the terminals inside the distributor caps. With the engine off, slowly turn over the motor until you are at the point where the spark should occur at idle speed, a few degrees before TDC. Remove the distributor cap and make sure the rotor is pointing to the correct plug wire terminal, maybe even a little past it. If the relationship is not correct - rotor position a little ahead of the cap terminal - as the engine speed increases, the advance mechanism will move the spark event earlier. If it happens when the rotor is too far away from the correct cap contact, the spark will jump to the wrong cylinder - popping and backfireing.
     
  3. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,367
    NY
    #3 Steve King, Jan 31, 2010
    Using a timing light have you check the advance in each dizzy. Does it go to 35* at 6000 rpm. You changed 2 things at once so you don't know if the carbs or the pertronix has caused the problem. Do we assume that you did not have this problem with the points . I would start over again with the dizzy installation. Set the flywheel to "0" on cyl. 1-4 and verify rotor position centered on the red dot on the dizzy. Then do the same on 5-8. Start it up and then set both dizzy's at 7*BTDC and get the idle at 1000 rpm. Verify that the timing is dead on and not jumping around at idle. Your idle should be nice and smooth. Smell the exhaust and see how rich it is. If you have a miss in the exhaust you most likely have either a carb adjustment problem or you have a fouled plug. Also on a high rpm miss or backfire you may have a bad sparkplug wire or extender. Keep us informed as to what you find. I have a pertronix unit installed in my 77 and have not touched it since I installed it in 2000. Good luck
     
  4. decardona

    decardona Formula 3

    Apr 23, 2005
    1,019
    PA
    Full Name:
    Dennis Cardona
    #4 decardona, Jan 31, 2010
    Thanks for the advice. I did not have a problem with a misfire with the points, so it has occured with the change over. Dialed the carbs back today to check misfire and now it is fine at high rpm, but sputters and pops while getting up to the higher rpm's. It is fine at a steady rpm. Don't know if I leaned it out too much or not, but I will check the timing as you have laid out and report back.
     
  5. tommott77

    tommott77 Formula Junior

    Feb 1, 2009
    652
    NC
    Full Name:
    Tom
    #5 tommott77, Feb 1, 2010
    Please report back once fixed as I am having a somewhat similar problem.

    Thanks
     
  6. decardona

    decardona Formula 3

    Apr 23, 2005
    1,019
    PA
    Full Name:
    Dennis Cardona
    #6 decardona, Feb 7, 2010
    Well, I started back at the beginning with the distributors. I checked timing with a timing light and it was a bit off. After the task of getting the timing right, the idle on the car was smooth and steady. Took it out for a test drive and had a bit of popping. After about 20 minutes, the popping went away. The next day, I started the car and again the idle was smooth, but, since I didn't go out the road due to weather, I ran the car and brought the revs up and down in a steady pattern. It was still popping and smelled as it if was rich. So I dialed the carbs back some to the point of no backfiring. It now runs smooth going thru thre revs when stationary. I am going to have to wait till the roads clear to test it under fire. Hopefully this will be the last of my ignition troubles.
     

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