1972 Johnson 50 hp wont run past 3000 rpm

[michael37659]

Hello folks, i have a 1972 50 hp johnson that im having problems with.It starts very easy idles smooth,in neutral if i raise the throttle slowly it start start missing around 2500rpm and if i increase it up to 3000 it will then the rpms will drop back down to about 2200 and has a big miss in it.if i just nail the throttle down quick it will rev up to about 4500 rpm and i dont notice the miss in it.In gear goin down the lake wot the motor will only turn 3000 rpm and i down notice it missing.I took spark plugs out a min ago and the ceramic insulator was black on the one to the upper cyclinder and the lower one was light tan.I have checked both cyl. with a spark checker and have a great blue spark.I unhooked the tan temperture sensor and nothing improved.Any suggestions would be very much appeciated

 

[michael37659]

Re: 1972 Johnson 50 hp wont run past 3000 rpm

Hello folks,
Well i found my problem on why my engine wouldnt rev past 3000 rpm with a load on it.My voltage regulator/rectifier was bad.I unhooked it and it reved up like a dream,i replaced it and now it runs great.

 

[kenmyfam]

Re: 1972 Johnson 50 hp wont run past 3000 rpm

Glad to hear it.

 

[1996fishnfun]

Re: 1972 Johnson 50 hp wont run past 3000 rpm

I have a '01 50 hp Johnson with the same problem and came here searching for answers. At the encouragement of a buddy, I had just rebuilt the carbs. I had trouble starting the engine. When I did get it running, it wouldn't go past 3000 rpm. So I rode around like that for a bit, and all of a sudden it revved up to the normal 5800 rpm max and ran fine the rest of the day. I figured I had done something wrong, but that it had worked itself out. The next time I went to use the boat, it did the same thing. When I rebuilt the carbs, I had started by backing out the idle screws 3-1/2 turns like my SEALOC manual told me to do. It wouldn't start and idle unless I pushed the throttle open a little way. I thought I was giving it more gas, so I backed out the idle screws a little more, and it still wouldn't start normally. Once I got it running, I screwed the idle screw in for each carb [one at a time] and backed it out until the engine seemed to run smoother. I think they ended up being backed out 2-1/2 turns. Now it starts and idles smoothly and runs right past 3000 rpm on its way to 5800. I never would have figured the idle screw to affect the WOT performance. Live and learn. I only hope this helps someone else. I thnk when I was only able to start it by giving it more throttle, I was opening the butterflies and giving the engine more air to accommodate the too-rich idle mixture.