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Volvo 3.0L hesitates when I mash the throttle

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  • Volvo 3.0L hesitates when I mash the throttle

    Info on my engine label is as follows:
    3.0 GS MEFS
    I believe it is a 1999 or 2000 year model Volvo Penta engine on a Glastron SF175 boat. It runs fine at any speed but I cannot give it a fast change in throttle. From idle or even from 1/2 speed, if I open the throttle fast it stalls. It will recover and keep running if I quickly pull the throttle back. As long as I increase throttle very slowly, it keeps running and runs fine. What all have I tried?
    1. replaced plugs, wires, and distributor cap.
    2. Put in a Sierra carb kit, and then when that didn't fix it, I put in a Holley carb kit. I forgot to mention that it has a 2 barrel Holley carb.
    3. Adjusted mixture screws per manual, now each screw it approximately 1 turn from seat, which gives it the best vacuum and RPM.
    4. Checked vacuum which is 15" at idle.
    5. Also replaced carb fuel filter and added Seafoam to gas. Did not see anything suspicious on filter.
    Since it sounds like a faulty accelerator pump I have checked to see that it spurts two good streams of gas on advancing the throttle. I also set the gap to .015 as specified in manuals.
    Of interest to me is that a Holly forum on cars says that the power valve should be 1/2 the idle vacuum reading. Since mine is 15" at idle, that would mean a 7.5 power valve. Mine is a 3.5, which came in the renew kit. The one I removed also was a 3.5. Maybe this rule doesn't apply to marine carbs?? Anyone got other suggestions for me to try?
    Could timing not advancing properly cause this? I kind of ruled that out since it runs great at high speed if I just advance the throttle slowly to get it up to speed. Thanks for any ideas you have.

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    Re: Volvo 3.0L hesitates when I mash the throttle

    Does anyone out there have experience with the Holley power valves? Is there a difference in what's required in boats versus cars?