High Speed Engine Stutter/Shake (w/ !!VIDEO!!)

[Dos_Enchiladas]

Hi all! First time poster here. check out the video.

engine shaking
1999/2000 120Hp Mercury 2-stroke engine (4 cylinders)
you can hear the engine make a loud stuttering sound along with a strong kick/vibration. while running at full throttle. it happens twice and after the second time the operator slowed the engine down. this stuttering continued to happen every 30-60 seconds at much lower speeds as well. my hypothesis includes:
1)engine misfire
2)propeller imbalance(the prop upon closer inspection does have a slightly bent fin)
3) lower unit connections (drive shaft, splines, etc)
any feedback would be greatly appreciated. thanks guys.

 

[lprizman]

Do you have the motor all the way down and messing with the trim?

 

[lprizman]

What's the fuel ball doing during this??

 

[Dos_Enchiladas]

motor is all the way down. we were not operating the trim. Eventually i had the engine open and was watching the fuel flow through one of the clear filter tubes in there. seemed to be constant and steady.

 

[Faztbullet]

Thats electrical...I would try disconnecting rectifier first and check all ground on ignition mounting plate

 

[lprizman]

Yup....got to be an electrical gremlin...

Start simple with the grounds....maybe connected....but dirty....I'd remove...sand and reattach securely

 

[Jimwhall]

Hi all! First time poster here. check out the video.

engine shaking
1999/2000 120Hp Mercury 2-stroke engine (4 cylinders)
you can hear the engine make a loud stuttering sound along with a strong kick/vibration. while running at full throttle. it happens twice and after the second time the operator slowed the engine down. this stuttering continued to happen every 30-60 seconds at much lower speeds as well. my hypothesis includes:
1)engine misfire
2)propeller imbalance(the prop upon closer inspection does have a slightly bent fin)
3) lower unit connections (drive shaft, splines, etc)
any feedback would be greatly appreciated. thanks guys.

I am far from a skilled mechanic. However, I had similar symptoms to this on my Johnson 112 SPL. I ended up replacing the fuel lines from the engine all the way to the tank and it resolved.