73 Johnson 50hp high speed issue

1973 Johnson 50hp

Model number: 50ESL7J5
Serial number: E3460894

I have the above motor on my tin boat. It quit running last fall, so this year I changed all the fuel lines and connections, pulled the carbs and cleaned both of them. This motor is the one with the funny metal plenum with adjustment ports on the front and the linkage the connects to a rich/lean mixture knob on the front of the motor. I have spark at both cylinders, clean gas, oil, and Blue Stabil. Compression is 125/120. I also pulled the shift/throttle box and lubed that up as well.

It shifts and runs great! But I do not have any high end speed. I put it in gear, it starts to plane, and stays at that speed through full throttle motion. I can stop for a while fish and it fires right up, runs great, and the same thing happens again. It is running so much better than last year, just not getting up to top speed. I did notice the rich/lean mixture knob no longer seems to effect how it is running or smoking. What did I do or forget to hook up? All the linkages appear to be working correctly and with full range.

Thanks,
Jeff

Thanks in advance

Re: 73 Johnson 50hp high speed issue

More than likely, you are dropping a cylinder at high speed. Could be spark or fuel.