98 GTI vibration issue!

[CrabbyPunK]

My ‘98 GTI has the 720 motor. Has a pretty significant vibration. So much when running it will loosen the 4 top manifold nuts and flood hull with water. I took the jet pump assembly off and removed shaft to see if that was problem. Start back up vibration still there. No change at all. It doesn’t have a knock and runs great. Gets up and goes no issue and runs 52mph constant all day unless nuts come loose and like this last time 2 studs actually broke. This is the 3rd time out and does the same thing. 2 weeks ago was on water riding HARD for a good 5 hours then broke the studs. This weekend was on water for 1 hour and loosened up 1 nut and took on water. Would motor mounts cause this much vibration? Is the PTO balanced and that out of balance?

 

[GGuillot]

No balance shaft on that ski, I'd say it could be a twisted crankshaft? hard to say why it's vibrating that bad, check all the motor mounts, which I'm sure you have, and make sure they haven't deteriorated loose.

 

[Rabid]

2014 GTI 130 - Bad Vibration
Try this link says check jet pump area

 

[Rabid]

2013 GTI 130 Vibration

 

[CrabbyPunK]

2014 GTI 130 - Bad Vibration
Try this link says check jet pump area

I stated above I removed jet pump assembly as well as driveshaft.

 

[CrabbyPunK]

No balance shaft on that ski, I'd say it could be a twisted crankshaft? hard to say why it's vibrating that bad, check all the motor mounts, which I'm sure you have, and make sure they haven't deteriorated loose.

Yeah. I was hoping it wasn’t internal since it runs great. Just vibrates a lot. I ordered motor mounts and just received them yesterday. Going to change and hope they kill the vibration, if not completely 50% or better would be amazing.

 

[mikidymac]

The 720's do vibrate a lot.
The reason that the manifold studs break is because the lower pipe support bushings get worn and allow the pipe to vibrate too much.
Replace all the rubber pipe bushings and sleeves and use the LocTite and torque specs recommended in the manual