1993 Johnson GT 200 Venom vibration issues

concept10

Petty Officer 2nd Class
Joined
Jul 24, 2010
Messages
156
I have recently purchased a boat that's powered by a 1993 Johnson GT 200 Venom outboard (J200STLETF) and i'm having issues with vibrations while in gear up to around 2500 RPM. The vibrations are felt through the hull and is making me uncomfortable about the condition of the engine and/or lower unit.

The engine idles well out of the water at around 1100 RPM and 800-900 when in the water. I have checked compression twice (once before purchasing and today) and the readings are all 90 except one cylinder is 85-90. (I believe cylinder #2 - port side middle cylinder).

As far as the vibs are concerned, the prop doesn't have any knicks and is stainless steel 4 blade. The lower unit is an aftermarket SEI unit (unsure of the hours). I believe the vibrations are maybe an issue with the gearcase.

What is the best way to rule this out? My current troubleshooting plan was to remove the lower unit and start the engine on the flush hose, but I can't feel the vibrations on the trailer... only when the boat is in gear and moving.

Could it be the prop shaft? One cylinder not firing? Prop imbalance?

Thanks in advance for any suggestions or comments.
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
Re: 1993 Johnson GT 200 Venom vibration issues

You could drain the LU through a cloth and look for any metal shavings in fluid or on plug if it has a magnetic screw.
Ive had motors on certain boats that have bad resonance at certain low rpms and a prop change fixed it.
Maybe changing the tilt angle could change the resonance dynamics and thus confirm its just a resonance issue with that set up of outboard/motor/prop
 

boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
Re: 1993 Johnson GT 200 Venom vibration issues

Prop shaft could be bent and yes, the prop could be out of balance. Take it into a prop shop and have it checked.
 
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