Results 1 to 2 of 2
  1. #1
    Join Date
    Oct 2017

    Default Idle Mixture and Bog at 2200 rpm

    I've searched this forum and went through all the recommendations but still having the same problem. I have a 2000 Moomba Outback with the Indmar 5.7L with the Holley 600cfm (75021) carb, which has vacuum secondaries and automatic choke. Not being able to solve this problem stinks because it ruined my daughter's birthday party when I took her and friends boating and couldn't get them out on the water for tubing.

    I cannot get the idle mixture screws to work correctly (I screw them all the way in and the engine does not die), my idle hovers around 800-900 and I can't get it any lower. Last time I took it out, I had a major bog at 2200 rpm and couldn't get it up much faster. So, at idle, I clearly have too much fuel/air entering the carb. I thought it might be a power valve issue, but I replaced it and still have same problem. Here is what I did.

    Rebuilt carburetor after the throttle shafts were leaking so much air that I couldn't bring the idle down (1200 rpm). I got a new base plate from Holley last season and put it all together and it ran great until now.

    1) Checked timing - I'm at 10BTDC with the shunt engaged
    2) Set fuel floats so that inspection hole is even with fuel
    3) Checked secondary valves at transfer circuit (they are closed all the way - no transfer circuit showing - so not square, but if I open it any farther manually than it revs even higher)
    4) Checked Power Valve (I installed a 6.5 and a 7.5 and same problem - both hold vacuum)
    5) Checked for vacuum leaks (only leaks are around throttle shafts again - none anywhere else)
    6) Idle screw all the way
    7) Idle mixture screws can be screwed all the way in and it actually runs a little better

    I have about 20in of vacuum at idle and the bog only occurs under load in the water.

    What am I missing?

    I'm about ready to buy another carb and put it on. Since Holley doesn't sell a 75021 online, does anyone have any recommendations for a new carb that they used as a replacement?
    Last edited by kcooper04; 10-07-2017 at 06:26 PM. Reason: Add more information

  2. #2
    Join Date
    Aug 2011
    Commerce Lake, MI


    I think Engine Nut could help you if you send him a private message.

    Sent from my iPhone using Tapatalk
    2017 Moomba Craz

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts