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  1. #1
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    Question Pro Max 300 chokes under load

    Hello All,

    New member to S&F. My brother was the guy who spent time on S&F, but he was tragically struck and killed in November by a car so getting our boat up and running is a mission for me. The family wants to spread his ashes over the lake during a flyby with our gofaster buddies when the weather gets warmer.

    In late 2019 we went in together on an offshore cat - 30' Spectre with twin Pro Max 300's (I believe they're 1996 or 1998) & SportMasters.

    We had one powerhead refreshed and the other rebuilt (new rotating assembly). While the engines were being rebuilt, we had the fuel tanks replaced. During our first wet run we had the problem described below in the refreshed engine. After 5 visits back to the shop (a 4 hour haul each way), I still have the following issue.

    The starboard engine, while under load only, chokes and almost stalls between 2200-3000 RPM. 90% of the time it will catch itself, idle and start revving back up, but the other 10% of the time it stalls.
    - Engine revs in neutral no problem
    - Idles fine (if you can call a Pro Max at idle "fine" ;-). Will typically run at up to about 2000 RPM fine.
    - If I very gradually increase throttle, every once in a while I've been able to get up to speed. Once >3,500 RPM it runs fantastic.
    - We have tried the following:
    1) flush and flow test fuel system (from tank to manifold) - we're confident it's not due to limited fuel flow
    2) rebuilt low pressure (diaphragm) fuel pump
    3) new high pressure fuel pump
    4) swapped fuel pumps between engines - starboard engine still had problem
    5) swapped each ECU (CDI and EFI) between engines - starboard engine still had problem
    6) replaced fuel manifold and injectors
    7) cleaned main wire harness connector pins, separated them (split pins), reseated
    8) cleaned grounds
    9) swapped various sensors

    We're out of ideas after spending all of last year diagnosing, swapping parts and wet testing.

    I'm hoping that the S&F experts can help me out!

    Mike.

  2. #2
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    Have you tested or swapped the coils around at all? Also on one case I have heard of a stator issue on a similar motor doing some weird things.

  3. #3
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    I believe the mechanic swapped the coils and stator from a known good engine onto mine. Will double check.

    thanks!

    Quote Originally Posted by Lake rat Skater View Post
    Have you tested or swapped the coils around at all? Also on one case I have heard of a stator issue on a similar motor doing some weird things.

  4. #4
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    I think you may have a port piston in a starboard hole or vise versa....since the power head was "refreshed"

  5. #5
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    Bump, I am curious if you ever got this resolved and what the problem was?

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