Carburetor back fire

Discussion in 'Troubleshooting & Diagnosis' started by Justin79maro, Apr 10, 2017.

  1. Justin79maro

    Justin79maro Member

    88
    1
    Jan 15, 2015
    Bonne terre, missouri
    Correct. But it showed 90-95 on the compression test. Number 4 showed 0
     
  2. 71 rs BBC

    71 rs BBC Veteran Member

    470
    65
    Nov 28, 2016
    Indy
    If it's spitting fuel out the drivers side only you have a duel plane intake right? Is #4 on the drivers side intake port. With no compression on 4 is it the intake valve if it's a fuel plane it's a choice of four cylinders.
     
  3. Justin79maro

    Justin79maro Member

    88
    1
    Jan 15, 2015
    Bonne terre, missouri
    It looked like it was coming out of the driver side of the carb. But number 4 cylinder on th passanger side showed 0. Why are engines so confusing
     
  4. 71 rs BBC

    71 rs BBC Veteran Member

    470
    65
    Nov 28, 2016
    Indy
    On dual plane intakes the drivers side of the carb will feed 4 cylinders. Two on the drives side and two on the passenger side. I don't remember which cylinders are fed by which. If you look at the intake you can see which ports are higher than the others and trace it.
     
  5. Bandit723

    Bandit723 Veteran Member

    2,251
    262
    Oct 1, 2016
    Waupaca WI
    Still confused why number one wire has no spark when number 4 has no compression. at this point i would suspect a bent valve but a vacuum gauge reading would help the needle would be flicking all over the place.
     
  6. 71 rs BBC

    71 rs BBC Veteran Member

    470
    65
    Nov 28, 2016
    Indy
    Ya The needle would go nuts. How you checking for spark.
     
  7. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    8,813
    133
    Nov 4, 2004
    Ringgold, GA
    You can pop the valve cover and verify that both valves on #4 are fully seating, that both valve stems are even with each other. I'd be sticking a bore scope in that thing.
     
  8. 71 rs BBC

    71 rs BBC Veteran Member

    470
    65
    Nov 28, 2016
    Indy
    If you have a compression tester. Charge that cylinder with air and listen to see where it's coming out of. Carb, exhaust. Crank case. That'll cover both valves rings and piston.
     
  9. Justin79maro

    Justin79maro Member

    88
    1
    Jan 15, 2015
    Bonne terre, missouri
    I used a different gauge and number has 35. I pulled plug wires off to see if it made a difference and it did but yet the plugs were black like it wasn't firing. When I hooked a timing light to number 1 it showed my initial timing at 14*, when I would rev it up and hold it the light would go out and not come on until it idled again. I don't have most of the stuff to do the checks mentioned. But with a different compression tester all the other cylinders besides 4 showed over 100, around 125. It's a 383 stroker with vortec heads... shouldnt it read like 185? Tmr I'm going to stick a air hose to it and see if it leaks.
     
  10. 71 rs BBC

    71 rs BBC Veteran Member

    470
    65
    Nov 28, 2016
    Indy
    When you check the compression are you holding the throttle wide open. That lets it breathe for a true reading. Let it hit three or four times. Your numbers do seem low but that could be from the throttle being closed. Just to make sure your timing light isn't freaking out on ya try it on a different wire and rev it up to see if it goes out. Might be the light.
     

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