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  • Backfires

    Have installed a Holley 4412 on a 304 powered, 1600 series short school bus. a great improvement over stock. problem is, is that it now backfires occasionally. Other than looking for a vacum leak, does anyone have any other suggestions on what to do? It has #68 jets in it. Any ideas will be appreciated.

    Jon M. Ketter

  • #2
    Occasional backfires could be from running lean?
    Did it back fire before?

    What is a 4412?

    The only carburetors I have seen on 304 would be the Holley 2300, 2210 and a 2245

    I have seen someone use a ford carb that bolted right on but it ran so lean he melted a good motor?

    Here is a page on Holley carburetor ID.
    http://www.carbs.net/CarbID/HolleyID.htm
    [CENTER]1994 Buick RoadMaSSter Estate Wagon LT1/4L60E. White and Woodgrain Sleeper...PCM 16188051 With SS/V4P/Custom Tune! WOT 12.9 AFR!

    1990 Chevy Suburban Silverado 5.7L 2wd ECM 1227747 HiWay Lean Cruise 18.5 MPG and 12.5 to 1 AFR at WOT!

    1972 IH 1210 Isky Cammed Balenced 345 4 speed PCM 16197427 Project!

    [SIZE=3][B][URL="http://www.gearhead-efi.com/"]GearHead-EFI.com[/URL] EFI Conversions and Chip Tuners![/B][/SIZE]
    [B]May be all you need to know about EFI![/B]

    and I still help local JustIH members (for fun) free! :cool: [/CENTER]

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    • #3
      Mark, this is a 2300 series carb. 500cfm model. it has #68 jets. a 6.5 power valve and it is backfiring through the exhaust pipes. Got the ole WD40 out and can't find any vacum leaks. Timing is 5 degrees before and the plugs look a little black. I think I'm gonna try a set of #66's. Gotta come up with something quick am leaving for Bristol thursday afternoon.

      Jon

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      • #4
        I'm new to the world of Internationals but I would put a check your timing and make sure it is still where you want it. The vacuum pressure difference between the old carb and new carb may be enough to mangle your timing causing an occasional backfire. It maybe advancing your timming too far, or not enough. Also, if that carb has a powervalve I would change it after you get the timing right. One good backfire could blow it out. Good luck.

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        • #5
          Just put new donuts in the manifold and that seemed to cure the problem for the time being. John Tabor got me thinking about the fresh air charge sucking back through the leak and setting off the through fire as he called it. put one of those anti-backfire check valves in when I rebuilt it. It doesn't pop through the carb, just the pipes. Welcome to the world of Internationals, good nerves help.

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          • #6
            I have read a lot of John Tabor posts , he has been around.

            Glad that cured the problem but you know you were on the right track!
            When you said back fire in the exhaust and the plugs are black, seems like you still have a rich running truck?

            Haven't you seen trucks with a donut leak and not back fire?

            To much fuel and all the extra oxygen could cause that.
            Just my theory
            [CENTER]1994 Buick RoadMaSSter Estate Wagon LT1/4L60E. White and Woodgrain Sleeper...PCM 16188051 With SS/V4P/Custom Tune! WOT 12.9 AFR!

            1990 Chevy Suburban Silverado 5.7L 2wd ECM 1227747 HiWay Lean Cruise 18.5 MPG and 12.5 to 1 AFR at WOT!

            1972 IH 1210 Isky Cammed Balenced 345 4 speed PCM 16197427 Project!

            [SIZE=3][B][URL="http://www.gearhead-efi.com/"]GearHead-EFI.com[/URL] EFI Conversions and Chip Tuners![/B][/SIZE]
            [B]May be all you need to know about EFI![/B]

            and I still help local JustIH members (for fun) free! :cool: [/CENTER]

            Comment


            • #7
              MARK, IT HAS #68 IN IT NOW AND I THINK YOUR RIGHT, I'M GONNA PUT A SET OF #66 IN TOMORROW AND THEN CHECK THE PLUGS AFTER I GET TO BRISTOL. THERE IS A GREAT SPEED SHOP RIGHT ACROSS THE ROAD FROM WHERE WE CAMP AND THEY HANDLE EVERYTHING. A BUNCH OF GOOD OLE BOY'S. I'LL GIVE YOU A SHOUT WHEN I GET BACK AND LET YA KNOW HOW IT WENT.
              JON/DRIVER1

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