"I have a 1979 70 hp Johnson o
"I have a 1979 70 hp Johnson on a pontoon boat. After replacing a faulty rectifier and old plugs, my engine seemed to run great - except when I brought it up to over about 4000 RPMs. At that point the engine RPMs would increase, but the boat would slow down, as if the prop was cavitating. It would continue to run this way until I pulled back on the throttle. Then I'd begin to get propulsion again. When increasing the throttle again, but slowly, the same thing would happen. So, is this a hub slipping problem? I removed the prop, could not determine that the inside portion that accepts the splined prop shaft was loose in any way. I did wonder if the disk that sits just behind the prop (has a rubber coated side) could be causing the problem.
Thanks in advance for any suggestions!"
"I have a 1979 70 hp Johnson on a pontoon boat. After replacing a faulty rectifier and old plugs, my engine seemed to run great - except when I brought it up to over about 4000 RPMs. At that point the engine RPMs would increase, but the boat would slow down, as if the prop was cavitating. It would continue to run this way until I pulled back on the throttle. Then I'd begin to get propulsion again. When increasing the throttle again, but slowly, the same thing would happen. So, is this a hub slipping problem? I removed the prop, could not determine that the inside portion that accepts the splined prop shaft was loose in any way. I did wonder if the disk that sits just behind the prop (has a rubber coated side) could be causing the problem.
Thanks in advance for any suggestions!"