FIXED! Violent Vibration over 3500RPM 200hp 92? ocean runner

[v12mac]

Violent Vibration over 3500RPM 200hp 92? ocean runner

I have a pair 92? 200hp ocean runners and one is missing / running very rough at high speed. Everything is fine up to 3K RPM but when I push up over 3.6K or so I get a violent vibration. Very steady (no alarms) When I back off everything is fine again?.
Does anyone have any good trouble shooting steps to diagnose a problem that only happens under high speed / load?

Plugs are clean but worn.
Boat is stored on a trailer so no marine growth or bent prop.

Thanks,
Mac

P.S. I have a shop manual just looking for some ideas

 

[tashasdaddy]

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

bent prop shaft? check your compression, and spark.

 

[v12mac]

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

How do I check my spark at 40 mph?

 

[lyncraft_mechanic]

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

you can't check your spark at 40mph thats not only nearly impossible but it's also dangerous. check your spark either by running the engine on muffs or at the dock, you can buy a spark tester at your local auto parts store for around $12.00.the spark should easily jump a 7/16" gap and be bright blue. you could have blown a head gasket, check your compression and for signs of water entering any of your cylinders, usually one sign of water intrusion would be one or more abnormally clean spark plug(s). DO NOT RUN YOUR ENGINE BEYOND 1500RPM ON MUFFS OR WITH OUT AN ADEQUATE LOAD.

 

[jonesg]

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

How do I check my spark at 40 mph?

with a timing light.
it might not show 'quality' of spark ,
but will show no spark or breakdown over 3k rpm.

 

[v12mac]

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

Ya, my wife said no to the water skis and 2' rope Idea and no to the intertube ride with my tool box.

I have a nice inductive pick up timming light that I'll throw on each cyl to see if I can track it down. Good news with twins I can just swap parts till the problem goes over to the other motor! and whola! that is the broken part.

I ran a compresion test this afternoon, all cyl were with in 4psi of each other.

 

[CharlieB]

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

Just how worn out is the gap on those plugs?

Excessive spark plug gap will cause a miss at higher engine speeds/increasing engine load, and can cause terrible vibration.

 

[v12mac]

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

Re: Violent Vibration over 3500RPM 200hp 92? ocean runner

Charlie B nailed it. I threw in a set of plugs gaped to .030 and she is running like a top. The old plugs were worn as bad as .048

What threw me off is that I thought I had replaced them just a while back but it turns out that they were much older than I had thought.

Mac