76 Johnson 35hp HELP PLEASE

Discussion in 'Bubba's Outboards' started by etexun, Jun 24, 2008.

  1. etexun

    etexun New Member

    Messages:
    375
    State:
    Texas (Nea
    I have a 35hp 1976 Johnson. I bought it to put on my catfish boat. Let me sort of tell you the history. When I got it it was set up for controls. But I wanted a tiller motor. So I was able to make the change to a tiller off a 25hp motor. I think the tiller it a little short and would like to find a longer one if possible. It was a short shaft and I had to find an extension kit foir it. I was able to do that and it is now a long shaft motor. When I tried the crank it the motor cranked up as soon as I hit the switch. So I thought it was going to work out great. I replaced the water pump while I had it apart just so I would know it was ok. I tested it out and it pumped water out really good.
    Memorial day weekend we loaded up and went to the river. A bunch of friends and their boats and me and mine. Here I was with a deep wide flatbottom and a 35hp motor and it just didn't seem to have much speed. My GPS said it was going about 19mph. A friend and his 20hp went faster. I changed out the spark plugs to hotter plugs. That didnt work. Then it just died on my as we were heading out to run our lines.
    When I got back I checked it. No compression. I took the head apart. Blown head gasket. So I got to wondering if that might have been causing it to lose power. I put on a new head gasket. Took it out to a small lake to test it. After a couple passes across the lake, still at only about 20mph it quit. Blown head gasket. Oh, I forgot I had checked the compression after I had changed to the new gasket it was getting around 125 on each cylinder.
    I have a new gasket and will change that out again. But I know that isn't my problem. ANY IDEAS?
    I know its a long post. Just trying to fill in gaps.
     
  2. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    Think your problem is that you need to "true up" your heads. Normally you get a really flat object, like 1/4 inch plate glass and glue some strips of fine sandpaper onto it. You put your head on the sandpaper and rub it in a figure 8 rotation. After about 75 to 100 of these circles, look at the head. The shinny places are where you have trued the head. The dark, grudgy looking places are areas that are still low. You need to do this until you have a nice, clean edge on the cylinder head. If you don't true up the plate, you will blow every head gasket you put on the motor.
     

  3. etexun

    etexun New Member

    Messages:
    375
    State:
    Texas (Nea
    Thanks for telling me about trueing up the heads with sandpaper. I will do that. Any idea as to why it just didn't seem to push my boat better than 19-20 mph. I just didnt think that is was topping out as fast it should. My buddy has a 25 johnson. I checked his speed at 23 mph and we had it loaded down with gear and weights and he and I. Mine barely got 20mph before it shut down on me.
     
  4. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    Most boats are as different as people. Some have a cleaner hull, creating less drag and higher speeds. Some look light and weigh a ton. Some are more aerodynamic, or whatever it's called in water, resulting in higher speed. I would think that unless your into something like "around the world in 80 days", your speed is just about right. You may be able to fine tune the boat to get more, you may not. It is a fickle world. The addition of a whale tail may get you onto a plane a little faster and allow you to go faster, but your probably just about there for your boat.
     
  5. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    If its blowing those gaskets because of head warpage it is not going to get up to operating speed until that problem is fixed. It will run up there but it can't operate at 100% until that head is seated properly so do as lawerance suggested and repair the head before worrying about speed.