Reply To: ‘79 Johnson 25 hp

[Don]

Is this engine new to you, or have you owned it for awhile? If you have owned it, when was the last time it ran OK at high speeds.. I just want to review the symptoms: seems to run fine at low speeds, but lacks power at WOT, but does not miss/skip/misfire…. Do I have it right?
Sounds like you have checked sync/economizer linkage, and the timing is advancing fully against its rubber stop, and the economizer linkage is pushing the carb butterfly open fully. You are running the engine on a boat with a prop at WOT, which is how you are testing it? If so, what pitch prop do you have and what type/length boat is the engine on?
Try to avoid getting in too deep, or spending money on a powerpack unless you can confirm the engine is misfiring/losing spark. I suppose it is possible that the engine is just running on one cylinder, but you would have noticed a poor idle…I suppose it is also possible that the engine is “dropping a cylinder” at WOT, but I would think you would hear it drop out.
I am confused by your tach readings, so am not paying too much attention to that right now. Again, sometimes test equipment can be our worst enemy which causes us to make improper conclusions based on inaccurate test results.