1994 Johnson 50hp rebuild

[John Wiegerink]

I just completely rebuilt my power-head(bored, new pistons, rings, seals, gaskets, etc.) I removed the VRO and installed a mechanical fuel pump. I also had a set of brand new 40hp carb ready for mounting and stuck them on the motor. Now, you may be scratching your head, but I had my reasons for doing it. First, I had problems with the VRO and then with the motor. The reason for eliminating the VRO. Second, the motor never ran right from the day I bought it and I suspected it was a carb problem, but could never find it. I eve3n rebuilt the carbs twice. The 40hp carbs have a smaller throat, but that's okay by me and it might mean a little better fuel economy. The questions I have is: For fishing would I be better off with the stock 12 1/4 x 15 prop or go to a 13 1/4 x 13 or so prop. I want to troll slow and am not as concerned about high speed running. I have a 16.5 ft aluminum Sea-Nymph boat and before the rebuild I could never get the idle down enough(1000 rpm was as low as I could go) and keep the motor running to troll slow. I ran it on muffs and it runs fine, but I haven't taken it to the lake yet. I'd like to get the prop first as the old one is pretty ragged. Maybe I should have posted this on the prop forum.

 

[steelespike]

Re: 1994 Johnson 50hp rebuild

Yes this is really a prop question.You should read the stickies at the top of the prop section and the helps at the prop store page.
You may be able to get your prop repaired.then do a test run get us the prop size (usually on the barrel or under the nut) and the max rpm and speed.
with that base line we can make a prop suggestion.
Prop selection is aimed toward getting the motor near the top of its rated rpm range at wot.(wide open throttle)
You should be able to get the idle down to 700 to 750.If not slow enough
a trolling plate is a possibility.
By the way if those 40 hp carbs are too lean you may have to do another rebuild.

 

[John Wiegerink]

Re: 1994 Johnson 50hp rebuild

With the old carbs and before the rebuild I could never get the motor to idle below 1000 RPM for any length of time(3 or 4 minutes) and when it did it was not at all smooth. I spent $350.00 at a very good outboard repair shop and when I got it back it was no better than when I messed with it. On to the 40hp carb question. I figured as long as the carbs were throated smaller that my engine would be basically like a 40hp motor. It would get the same fuel to air ratio as the 40hp so it wouldn't be lean or rich. I remember back when the 9.9hp and the 15hp were the exact same upper unit and the only real difference between the two was the carburetion. So, wouldn't this be the same? Of course I could be wrong! My wife says that I'm wrong at least once a year. Ya, right!