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Thread: to much prop?

  1. #1

    Default to much prop?

    I have a 1989 Johnson 88 spl on a 1989 bumble bee 15` 4" bass boat. the motor runs fine, no problems. new fuel system, new water pump,and the compression checks at 117 lbs per cylinder. the problem is it won`t come out of the hole unless I send my son to the front of the boat to hold the nose down. once it planes off it runs fine except it will only run 4300 rpm max. if I trim the nose up the rpm will increase but it starts to porpus. the owner before me put a 12.5 X 21 4 blade stainless prop on and I think this is why I can`t get max rpm. what do you think?

  2. #2
    Join Date
    Sep 2006
    Location
    Baton rouge, La, USA
    Posts
    2,501

    Default Re: to much prop?

    what is the exact compression reading on each cylinder?..will the spark jump 7/16 inch om all cylinders with a spark gap tester?...

    is the cavitation even with the bottom of the hull?

    why did the previous owner get rid of the boat?did it perform like this for him?..what did he do with the original prop?..is it available?has the motor on it now always been on it?

    do you have the motor trimmed all the way down while trying to come out of the hole?you should not have to have it all the way down but want to know...

    what plugs are in the engine?

    when you pull the boat out of the water and get it on the trailer how much if any water comes out when you pull the drain plug?

    if everything meets above criteria which is good compression,good spark,motor mounted correctly,correct plugs in the engine and a dry hull I would put an inductive timing light in the boat and look at each cylinder for even fire when the boat is in the water under power...you may need someone to help you on this to make it easier although you can do it alone..just tape the trigger back on the timing light and place it beside you so you can see it..

    if all this is ok I would address the prop issue...I see no need for a 4 blade prop on that rig..

    good luck and get back to us please..i

  3. #3

    Default Re: to much prop?

    the compression checks at 117, 115, 116, and 115. the spark will jump 7/16 plus, the timing is right on. but I have found what may be my problem. the cavitation plate is 3 1/2" above the draft of the hull. could this be all of the problem, because everything checks out good?

  4. #4
    Join Date
    Sep 2006
    Location
    Baton rouge, La, USA
    Posts
    2,501

    Default Re: to much prop?

    yes...always fix what you see broke or wrong first...

  5. #5
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    2,581

    Default Re: to much prop?

    Too much prop...need a 19 or 20 pitch and vented....lowe motor so cavataion is 1-1-1/2" above pad. This is usually 1 hole above being mounted flat on transom
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  6. #6
    Join Date
    Dec 2015
    Location
    maplevalley WA
    Posts
    3,469

    Default Re: to much prop?

    Do you have a pic from the back of the cavitation plate faceing straigt forward with the engine down? Get a photobucket account (free) and upload the pics there and then link them here.

  7. #7
    Join Date
    May 2011
    Location
    slough ,berkshire uk
    Posts
    155

    Default Re: to much prop?

    your prop is too small in diameter for the v4 on that boat.
    its a v hull with a pad or high speed, pro to sty up but needs more dameter.
    what is the prop exactly, make and part number would be good. ,

    if it is a Solas prop then you have the answer.

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