96 Sugar Sand Mirage Sport - Sportjet 120 Vibration

cdness

Cadet
Joined
Jun 25, 2012
Messages
8
I have done lots of reading on the SportJet 120 on these forums and others. I have also stopped in at the local repair shops to chat with the mechanics an even shop managers to see if I can get some direction on this issue. The forums have been more helpful, but I would like to confirm my suspicions...

The boat starts, idles, and drives perfectly fine, except at WOT. I can be at 90% and it is fine, but that last little bit causes the motor to make a sound like something just isn't right. It sounds and feels like a vibration coming from the motor somewhere or like the boat is losing power and or cavitating... I don't have a better way to explain it unfortunately.

I have read that the rev limiters can go bad on the Force 120 motor, but my boat doesn't have a tach. I am going to go look for one used at the local salvage so I can hook it upto the motor to see where I am running. Does anyone here know what the reference RPM should be at WOT? Also do you know what wire is the tach wire on this motor?

I know there is some wear on the wear ring from the previous owners. I was hoping to get another season out of it before having to look into a rebuild. I know that will cause performance issues, but can it also cause the vibration noise?
 

hypersniper

Banned
Joined
Jun 18, 2011
Messages
104
Re: 96 Sugar Sand Mirage Sport - Sportjet 120 Vibration

well if you happen to rev it too much and it blows up. im looking for a flywheel.... if the rev limiter goes bad you will not get spark. thats how they go bad.
 

cdness

Cadet
Joined
Jun 25, 2012
Messages
8
Re: 96 Sugar Sand Mirage Sport - Sportjet 120 Vibration

well if you happen to rev it too much and it blows up. im looking for a flywheel.... if the rev limiter goes bad you will not get spark. thats how they go bad.

Ha ha funny... If I find a flywheel I'll be sure to let you know.

So location of the tach wire and reference RPM at WOT anyone?
 

aksor

Petty Officer 2nd Class
Joined
Apr 21, 2009
Messages
150
Re: 96 Sugar Sand Mirage Sport - Sportjet 120 Vibration

Tach wire should be gray and it comes from the voltage regulator and wot should be 5100 rpm
 

cdness

Cadet
Joined
Jun 25, 2012
Messages
8
Re: 96 Sugar Sand Mirage Sport - Sportjet 120 Vibration

Thanks aksor! This is exactly what I am looking for.
 

Anders67

Petty Officer 2nd Class
Joined
May 23, 2012
Messages
117
Re: 96 Sugar Sand Mirage Sport - Sportjet 120 Vibration

The rev limiter you can just disconect. And se if it stops doing that.

Have exact same boat :) . Same year.




Try to find out if it?s sucking air in the jet pump/ cavitating, debris in inlet . = pump problem

Ore if it is the engine that is the problem. = engine problem
 

cdness

Cadet
Joined
Jun 25, 2012
Messages
8
Re: 96 Sugar Sand Mirage Sport - Sportjet 120 Vibration

Cool! I will do some more checking when i get to the lake in a few weeks and update the thread. Ill be verifying the ride plate for seal while it is on the lift. Thanks for the reccomendations.
 

Anders67

Petty Officer 2nd Class
Joined
May 23, 2012
Messages
117
Re: 96 Sugar Sand Mirage Sport - Sportjet 120 Vibration

I have done lots of reading on the SportJet 120 on these forums and others. I have also stopped in at the local repair shops to chat with the mechanics an even shop managers to see if I can get some direction on this issue. The forums have been more helpful, but I would like to confirm my suspicions...

The boat starts, idles, and drives perfectly fine, except at WOT. I can be at 90% and it is fine, but that last little bit causes the motor to make a sound like something just isn't right. It sounds and feels like a vibration coming from the motor somewhere or like the boat is losing power and or cavitating... I don't have a better way to explain it unfortunately.

I have read that the rev limiters can go bad on the Force 120 motor, but my boat doesn't have a tach. I am going to go look for one used at the local salvage so I can hook it upto the motor to see where I am running. Does anyone here know what the reference RPM should be at WOT? Also do you know what wire is the tach wire on this motor?

I know there is some wear on the wear ring from the previous owners. I was hoping to get another season out of it before having to look into a rebuild. I know that will cause performance issues, but can it also cause the vibration noise?


I had a little stone stucked once in mine impeller, and some plastic that was in whater sucked in. An it vibrate a lot when you try to reving up.



If it?s the pump unit:

Check for stucked debris in whater inlet.

Check wear ring.

Check for broken/ leaking gasket betveen boat/jetpump and ridplate ok .

Check impeller for bent blade ore some stucked objekt.



Engine:

First.

Fuelflow / filter to carbs / hoses and fuelpump. The tin evapor-lines on left side carbs not blocked.

Carbs okay and tuned in right way.

Timing.



Try that first.



Regards Anders
 
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