I have a 1975 Johsnon 2-Stroke 9.9 that is giving me fits. I just aborted a 10-day river trip at the boat ramp because of it. I just installed a new water pump last week-old one had quit pumping. Yesterday, I ran it lifted about 8 inches above the transom (a very common practice here, in AK), but, at wide WOT, that caused the water pump intakes to be out of the water. I had to run it dry for about 30 seconds (at WOT-the current was carrying me away.) I put the engine back on the transom and it ran fine at idle and pumped water. So that's the back story. Then, I took it back into the river, and ran it at WOT. It started misfiring and shuddering about every half second or so. It vibrated hard enough that I could feel it in bottom of the boat. It runs good below WOT, but I need max power to make headway upriver.
Anyone have any ideas on a possible or probably cause? Is this connected to running the water pump dry? Ethanol fuel? Something totally unrelated?
Anyone have any ideas on a possible or probably cause? Is this connected to running the water pump dry? Ethanol fuel? Something totally unrelated?