Thank you for your quick response. it is quite a jolt, and it only happens when the boat is in gear and i start to go fast. it gets to the point where it happens so frequently that the motor goes ratt an tatatat rat ta tatttatatt, and starts shaking violently. I think you could be right about the clutch dog. I am a novice at this stuff, I am a salesman by trade (a good one at that) but i think i am going to try and do this myself. 3 people have worked on this boat since i have had it. John from Pt. Reyes (retired UPS driver who knows a lot about old john sons) he replaced the fuel tanks, the rope pully system to steel cables and got the engine running. he died. then John from Sebastapol, a retired SFSU professor, he tuned up the motor, replaced the throttle cables and mounted the lights on the trailer, he just got cancer so he only helps me via FaceTime. now my neighbors son who is a mobile tractor mechanic is working on it, but he charges 100 bucks an hour, 500 to replace the starter 2 weeks ago. we went out on the boat so he could diagnose the problem, and he said it could be carb, could be ignition etc etc. is there a way i could post a quick video to show you what the engine is doing. I watched a video on clutch dogs and it involved machine type corrections to the gears. that looks pretty intimidating to me. I could post the video on Facebook or maybe instagram.