Exhaust Popping between 3800 & 4200 RPM's
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Exhaust Popping between 3800 & 4200 RPM's

  1. #1
    Senior Member PonyFiveO's Avatar
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    Default Exhaust Popping between 3800 & 4200 RPM's **UPDATE!**

    **UPDATE!** See#10

    Howdy All! I am hopping you can help me diagnose this. My brothers boat seems to be popping out the exhaust between 3800 and 4200 RPM's or so. You put the pedal to the floor and it will push past the popping to cruise at 4800 RPM's (Pump Probably Getting Loose =) without as much as a hiccup. It was fine when we put it away from a day at the lake, then next time we took it out it popped. Since it started, New Cap, New Rotor, New Plugs, New Wires, New Coil. This last time it ran, past Saturday at Modesto, I re-gapped the plugs from .045 to .037/36 with no change. The plugs did look cleaner towards the back of the engine while the the ones near the front were darker. Thoughts on where I should start?

    Stats: 79' Nordic Bubble Deck, Stock 454, Air Gap Intake, HEI, Vacuum Holley 750, Stock Dominator Pump, OT Headers.

    Thanks!
    Last edited by PonyFiveO; 08-05-2018 at 03:52 PM.

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    Quote Originally Posted by PonyFiveO View Post
    Howdy All! I am hopping you can help me diagnose this. My brothers boat seems to be bopping out the exhaust, only between 3800 and 4200 RPM's of so. You put the pedal to the floor and it will push past the popping to cruise at 4800 RPM's (Pump Probably Getting Loose =) without as much as a hiccup. It was fine when we put it away from a day at the lake, then next time we took it out it popped. Since it started, New Cap, New Rotor, New Plugs, New Wires, New Coil. This last time it ran, past Saturday at Modesto, I re-gapped the plugs from .045 to .037/36 with no change. The plugs did look cleaner towards the back of the engine while the the ones near the front were darker. Thoughts on where I should start?

    Stats: 79' Nordic Bubble Deck, Stock 454, Air Gap Intake, HEI, Vacuum Holley 750, Stock Dominator Pump, OT Headers.

    Thanks!
    .
    Magnetic Contact in the Dizzy..Had the same problem with MSD

  4. #3
    Seriously off center slowride's Avatar
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    Quote Originally Posted by PonyFiveO View Post
    Howdy All! I am hopping you can help me diagnose this. My brothers boat seems to be bopping out the exhaust, only between 3800 and 4200 RPM's of so. You put the pedal to the floor and it will push past the popping to cruise at 4800 RPM's (Pump Probably Getting Loose =) without as much as a hiccup. It was fine when we put it away from a day at the lake, then next time we took it out it popped. Since it started, New Cap, New Rotor, New Plugs, New Wires, New Coil. This last time it ran, past Saturday at Modesto, I re-gapped the plugs from .045 to .037/36 with no change. The plugs did look cleaner towards the back of the engine while the the ones near the front were darker. Thoughts on where I should start?

    Stats: 79' Nordic Bubble Deck, Stock 454, Air Gap Intake, HEI, Vacuum Holley 750, Stock Dominator Pump, OT Headers.

    Thanks!
    VAcuum secondary carbs tend to do that in transition to the secondaries on jets. Fatten the primaries a tad, go softer spring or mechanical secondary.






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    Senior Member PonyFiveO's Avatar
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    Thanks Guys. I think I will do both. Go up two in Jets and probably just replace the distributor with this...

    https://www.ebay.com/itm/Racing-Chev...8AAOSwpFlaOx0K

    Hopefully that will be the last of the popping

  7. #5
    Senior Member Daddy B's Avatar
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    Quote Originally Posted by PonyFiveO View Post
    Thanks Guys. I think I will do both. Go up two in Jets and probably just replace the distributor with this...

    https://www.ebay.com/itm/Racing-Chev...8AAOSwpFlaOx0K

    Hopefully that will be the last of the popping

    My bbc started popping like that through the carbs when the cam started going flat then worsened. check valve adjustment and if looose it is bad news.

  8. #6
    Senior Member LiquidDan's Avatar
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    Quote Originally Posted by PonyFiveO View Post
    Thanks Guys. I think I will do both. Go up two in Jets and probably just replace the distributor with this...

    https://www.ebay.com/itm/Racing-Chev...8AAOSwpFlaOx0K

    Hopefully that will be the last of the popping
    Might want to do one at a time so you pinpoint the problem IMO
    Originally Posted by gn7 "Stick to making the worlds best engine stand."

  9. #7
    Seriously off center slowride's Avatar
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    Quote Originally Posted by PonyFiveO View Post
    Thanks Guys. I think I will do both. Go up two in Jets and probably just replace the distributor with this...

    https://www.ebay.com/itm/Racing-Chev...8AAOSwpFlaOx0K

    Hopefully that will be the last of the popping
    Don't waste your money on a distributor. Jets don't want a vacuum advance and all your advance should be in by around 2000 rpm. I would put a timing light to it and increase rpm until all the advance is in to see where you're all in. You should find you are all in WELL before your issue starts. Find a known good double pumper and try it out..... I think you'll find your cause.






  10. #8
    Senior Member Heatseeker's Avatar
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    Cool

    Didn't you used to have a boat called...Heatseeker?

    If you are truly popping out of the exhaust, I would recommend removing the valve covers and checking valve lash. That can be a symptom of cam lobes flattening... Better to find it early before all the lobe material gets sent through the engine.
    Last edited by Heatseeker; 07-12-2018 at 10:28 AM.

  11. #9
    Senior Member PonyFiveO's Avatar
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    Howdy All!


    Sorry it took so long to reply. Life in the way, so still haven't had a chance to look into it yet for an update. In regards to the flattening cam lobes, if it was doing this, would it still allow me to rev past the popping (3800 to 4200 rpm) and cruise smoothly at 4800 rpm? I was test driving a boat once that was found out later to have a flat cam, and it couldn't rev past 3500 rpm no matter what the owner tried.



    Hi Heatseeker! Yup its me. Just getting back into things. How are you doing? Still doing your thing?

  12. #10
    Senior Member PonyFiveO's Avatar
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    Default Problem Solved!

    And the Winner is... Gone Green!

    We replaced the distributor and the popping is gone. Thanks!

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