Need help

Discussion in 'Propulsion' started by brutus, Sep 11, 2007.

  1. brutus
    Joined: Sep 2007
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Vancouver

    brutus New Member

    I have a gm 350 stroked to 383 with a holley carb. When crusing at 4000 rpm the boat runs fine but anything over 4200 it starts to backfire or popping the engine builder said we can get upto 5200 rpm I don't know what to do to fix this problem any help would be very usefull
  2. Frosty

    Frosty Previous Member

    Fuel starvation. Check out all fuel lines, filters, breathers, pump etc etc
  3. saabster
    Joined: Mar 2007
    Posts: 15
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: UK

    saabster Junior Member


    try increasing your fuel line size.i hav a 350 tuned up to 330hp, increased fuel line to 12mm. runs brillant.
  4. thudpucker
    Joined: Jul 2007
    Posts: 885
    Likes: 31, Points: 0, Legacy Rep: 453
    Location: Al.

    thudpucker Senior Member

    Fuel starving sounds good to me too.
    I also wonder about the Points bouncing. Do you have a Breaker Point distributor?

  5. TerryKing
    Joined: Feb 2007
    Posts: 595
    Likes: 25, Points: 28, Legacy Rep: 289
    Location: Topsham, Vermont

    TerryKing On The Water SOON


    Backfiring intermittently sounds more like ignition than fuel. Fuel starvation = too lean, right? Usually a leaned out engine smoothly loses power. Unless the lean mixture causes preignition, maybe.

    Fuel filters clean?

    What do the plugs look like if you shut down after running at 4000 for a while, and pull a couple plugs?

    Is this a Holley 2-barrel? I have one on my 350. If I shut the fuel pump off, the engine surges and loses power before stopping. But it doesn't pop and backfire...
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