Reply To: Expert Diagnosis: Expertise genuinely appreciated

[rschrull]

Thanks Tubs. I did in the original post (Bobby Johnson tuned the motor but did not go further and note that what happened in the video also happened in his tank). Reading carefully the post, one would usually conclude the running on one cylinder is solved. Post question was focused on what the tump/jerk is. But anyway, turns out it is not the clutch dog. Removed. It’s fine. All lower unit checks out with little to no play anywhere. No worn gears, or metal in the gear oil. Ignition absolutely perfect thanks to Bobby. Other things done. Packers replaced. Carb is service/checked and fine. Bobby adjusted the low and high speed in his tank under and in gear, although not on the water, so should be a final adjustment under power as I have done with another boat and motor I have. This is entirely something different and all I’ve been able to research points to some kind of leak in the crankcase. But the internet, reddit posts and FB groups isn’t the best place to research this kind of stuff. It’s like the wild west. That’s why I’m here on this forum, as I’m told experience resides here.  “AI (Claude) research concludes that because there is no change in RPM when this occurs, a clutch skip can’t happen without the engine briefly losing its load. That if the prop shaft disconnects, even for a fraction of a second, the engine always reacts to that with a momentary flare. Flat RPM through the clunk means drive was never interrupted. Whatever is banging, it’s downstream or outside the driveline.  I don’t buy it, my gut is, that it is upstream in the powerhead.  Maybe this forum isn’t the place to resolve this challenge? I openly wonder. Perhaps the ideal place is to be side by side with an older someone who has lived with these engines and is willing to and earnestly desires to take the time to go through it all with someone new to the engines, to pass on what they have learned over the years, while at the same time fixing the problem.