Re: 1957 johnson still won’t run right

[David Stanton]

Just a thought, When the boat slowed down, was the shaking you described accompanied by the motor trying to rev to higher RPM’s like it went into neutral? When it revs high, the rev limiter starts cutting out one cylinder which will make it "shake and chunk" like crazy until the RPM comes down by reducing throttle. If so, I’d bet the prop is slipping on it’s thin rubber shock absorbing mount to it’s hub. The fix is to replace the prop. Taking it off, you won’t be able to slip it by hand. You can mark the prop’s position on its hub, put it back on, let it shake/fail again and then see if the prop moved on the mark you made. It’s unlikely it will stop at the same place on the hub. There used to be shops that could replace this rubber hub to prop interface, but I haven’t heard of one for decades. You can get a new prop reasonable at http://www.propcopropellers.com/.
Dave