Dr Go knows this story. Two years ago I had a 135hp Evinrude on a 15ft Tomahawk that was at the Lake Kosh show. The motor would start, sputter etc. Had to leave it tied to the dock and took a ride with Paul in his Loanstar. Turns out it was the pickup tube in the portable fuel tank that had collapsed/bent, nothing with the motor at all. After fixing that problem she topped out at over 50 mph. That's the good Dr. with his Admiral in the background polishing the brass.
The Johnson motor that wavered at slow speed was on a Bee Craft tri-hull. Beautiful boat set up for fishing.