Need Help with 1974 V4 Johnson

Discussion in 'Bubba's Outboards' started by NEPATRIOTS, Oct 21, 2009.

  1. NEPATRIOTS

    NEPATRIOTS New Member

    Messages:
    11
    State:
    FL
    I'm new to the board also i'm hoping to get some help with my motor. I have a 74 Johnson V4 85hp, the motor is on an 18 foot Cobia open bow Boat Dry is 1,500. My problem is at WOT i'm only getting 3000 RPM, the Prop is 13 x 17. Had the boat out the other night, It wouldn't plain until my buddy got up front but that only raised the rpm to 4000. Motor starts good and idles good at the dock under load in. Neutral it will rev to 5200 but in gear only 3000
     
    Last edited: Oct 21, 2009
  2. catwhisper

    catwhisper New Member

    Messages:
    456
    State:
    georgia
    did the motor come on the boat? if the foot is to far below the bottom of the boat it will do that. or trim is not adjusted correctly. if it dont have power trim may have to adjust it manually and try it. Bye the way Welcome to the BOC You'll have fun and learn alot.
     

  3. NEPATRIOTS

    NEPATRIOTS New Member

    Messages:
    11
    State:
    FL
    My cavitation plate is about one inch higher than the bottom of the transom.
     
  4. bluejay

    bluejay Well-Known Member

    Messages:
    8,493
    State:
    Napoleon, Mo.
    Welcome to the BOC Frank.
     
  5. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    See if you can find a 15 prop and try that. Your motor heigth is alright at the height you have it now. First I want you to do a compression ck and spart test and make sure its hitting on all four. I have one of those old 85s they are good strong engines. Mine was on a smaller Bass boat with the weight you are trying to push you need to lower the size of your prop.
     
  6. NEPATRIOTS

    NEPATRIOTS New Member

    Messages:
    11
    State:
    FL

    Bubbakat thanks you are the person i really wanted to address this to, I joined this site because of reading your posts i believe you to me very knowledgeable with marine motors. I did the compression test today got 120 on 3 cylinders and 115 on the 4th, After we tested the compression we started the motor and took off one plug at a time, the motor responded with a drop in RPM. I just took it out with a 13 x 15 prop and moved the motor one hole from the transom the boat finally plained right away and got 4200 RPM. While riding at 4200 RPM the motor seemed to want to go more with a pulse of energy here and there. Could the carbs or fuel pump need some attention. Again thank you for your response to my outboard problem.
     
  7. playin4funami

    playin4funami New Member

    Messages:
    4,104
    State:
    Saronville Ne.
    sounds like a fuel problem with the surging,my first guess is change out the fuel line and primer bulb with new and add a inline filter,also drain the fuel tank and I'll bet theres some water and junk in there,then your floats could be sticking and not delivering fuel right either.
     
  8. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Look on the bottom of the carb bowels and you will see a hex head brass screw. Take them out one at a time and run you a pisice of thin wire upinto them. That is where the High speed jets set. When you are done check the fuel pick up tube in the bottom of the fuel tank. If the lines are old and hard replace all of them. I would get me a can of sea foam to run in the fuel to help clean the system and put in an inline filter. That engine runs good on QL77JC4 CHAMPION SPARK PLUGS. If it is surging at higher speeds is is most likley fuel related. Once we get this cleared up and she runs good I'll tell you how to tune that prop to do better. Oh gap those plugs at 35.
    Those old v4s wouldn't idle to smooth because it had steel reed valves. You can purchase compost reed valves to make it idle and respond better on the throttle.
     
  9. NEPATRIOTS

    NEPATRIOTS New Member

    Messages:
    11
    State:
    FL
    The tanks are aluminum and the filter is a new water separator, Im not sure if I can take the pickup tube out of the Aluminum tank it looks welded on the top, Can I run sea Foam in the tank of gas or will that cause a problem, not sure if the sea foam will clean the pickup tube.
     
  10. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    That pick up tube should screw out Mine does on my alum. tank but in case it doesn't , yes go ahead and add some sea foam to the fuel. No seafoam doesn' hurt to use it all the time. It will keep the engine decarbed and the fuel system clean. Take you some compressed air and blow back into the tank on the fuel line and if there is any gum loaded on it after the sea foam gets to it for awhile it will turn loose.
    Do the carbs like we talked about and try that if that doesn't do it then we will start on the fuel lines.
    Good for you on the fuel water seperator. Don't ever bypass that.


    OH one more thing look at your fuel pump there should be a screw in the center of it. Take it out and clean the screen that is behind it.
     
    Last edited: Oct 22, 2009
  11. NEPATRIOTS

    NEPATRIOTS New Member

    Messages:
    11
    State:
    FL
    Thank you Bubbakat, I did the carbs and Blew air through the Pickup tube, I got a can of sea foam and added it to the Fuel tank,I got a kit and we rebuilt the fuel pump as well. I will let you know Tomorrow how it ran as I will be taking the boat out later this evening. I wanted to let you know when I got the boat in may I took everything apart as I restored this Cobia, I had both tanks out and changed everything on them as I put new WEMA sending units in both Tanks, so all the fuel lines are new, anyway let me keep with your advice since you know a lot more about this than me and I will let you know how it ran tomorrow. Again Thank you very much for all you have done so far.
     
  12. NEPATRIOTS

    NEPATRIOTS New Member

    Messages:
    11
    State:
    FL
    I took the boat out tonight and I can't thank you enough, I did what you said with the wire in the carb Jet, used the sea foam and replaced the plugs and gapped them as you requested, and wow what a change. At first the Motor was still surging a bit but the more we drove it the better it became, the Motor hit 5300 Rpm and we topped out at 50 mph by GPS. The rest of the evening the Motor just ran like a champ. Thank you so much for your help, my wife and the kids really enjoyed going out tonight with the boat, It's people like you that make America Great. Tonight we got two Snook and three tarpon with live bait, but I cannot tell a lie the wife outfished me big time as I only got 1 :sad2:
    Again I can't say it enough THANK YOU BUBBAKAT YOUR THE BEST.
     
  13. Smittydidit

    Smittydidit New Member

    Messages:
    4
    State:
    nc
    I have a 82 v4 had some what the same problem.Sometime it would surge and sound like it had some more power but just would not take off on all 4. Mine was a spark plug wire problem. It has them 3 piece spark plugs with the spring in the end and just would not make contact all the . New wire fixed the problem.Good luck