73 9.5HP johnson looses RPM intermittent

[bowtieboy77]

I have a 73 johnson 9.5hp it starts and runs great in all temp ranges even in well below freezing temps. The problem is when I take it to WOT some times all my rpms is there other times it is underpowered like I lost a few hundred rpms. If I back off the throttle for awhile after it acts up and return to WOT it might be the same or it might have all its power back. At all times of motor operation it is running smooth and never seems to be missing just a lack of some rpms. Any help is greatly appreciated. Also what is the average WOT rpm of this year of motor as I would like to measure rpms with my optic tach.

 

[tomcat8186]

Re: 73 9.5HP johnson looses RPM intermittent

I had a similar problem with my 1986 9.9. It was a bad plug wire. I replaced both wires and cleaned both coil connectors. It worked for me. I was surprized to see how well it ran on only one cylinder.