I have an old 15' Larson runabout with a 28hp Johnson longshaft outboard. See link below for photos.
It is obiously badly underpowered but I don't have the cash for another motor. I'm trying to milk every mph I can out of it. Last year we maxed at about 18-20 (GPS) with just 2 people after trying everything I could think of. A third person just killed it. Compression is good, tilt is at best of the setting,s and hydrofoil was put on. Not sure if the prop is the best. It is bigger and the blades fatter than the one that came on it. Got it off a Johnson 25 I had in the shed. Does seem to plane after a few minutes and you can here the rpms rise when it does.
Here is my question, This may not be true, but it feels like I could get a little more rpms and that the throttle 'may' not be opening her up all the way. In other words, when it stops moving forward, I wonder if the linkage being incorrect and holding it back any. Because I messed with the linkage it may very well not be right. So before taking it to a marina at $90 an hour for something they can probably spot in 30 seconds, is there a quick procedure or description of what direction or what way I can adjust this to see if it is all the way open? It also has a manual spark advance level as the one picture shows. Before I figured out how that worked we were doing 10 mph So also, since that moves things forward before starting, could that also not be adjusted all the way out and maybe bump up the rpms? Perhaps there is another post that might have some close up photos that could give me the general idea of what to try. If I could get 3-4 more mph I'd be thrilled.