Yamaha 130HP 2 strokes shaking 800 to 1000 rpm

[fmt2bx]

Hi!
I have this 1990 130HP Yamaha 2 strokes 130ETXD.
Symptoms:
Idle set at 750rpm, gives me 600/650 when in gear (smooth idle). I advance the throttle slowly and between 800 to 1000/1100 rpm the motor shakes enough to shake the whole boat. Passed 1200rpm, runs great. Cold or hot no difference.

What I have done so far:

1- Removed carbs, cleaned with ultrasonic and set floats at 16mm as per manual. and idle mixture screw set at 7/8 out.
2- Inspected the reeds while carb out, they appeared to be fine.
3- Set the ignition timing as per manual, rods at 53mm and 60 mm. 4 deg ATDC alined the mark on flywheel with trigger mark. set WOT timing at 22 deg BTDC and align mark as well.
Once timing set statically, verified with timing light and it gave me 5 deg ATDC at idle (manual says it should be at 5 deg, so all good there)
4- With carbs mounted, checked the sync and no adjustment needed there. No play either
5- Idle speed screw removed, set the throttle roller to throttle cam as per manual.
6- Started motor and adjusted Idle rpm to 750 in neutral.

7- Fuel pump replaced, not that the old one was bad but that is part of my preventive mx.
8 Checked compression, 125psi on all 4, it has been like this for the past 3 years, no changes there.
9- Did a decarb with seafoam and replaced spark plugs.

So this is where I am and still giving me some shaking between 800 and 1000 rpm.


There is 2 things that I found out while performing the work:

1- The throttle roller has a flat spot
2- After adjusting the timing as per manual, I am a bit dumfounded. After setting the roller with idle screw off, once idle speed adjusted to 750rpm, the roller isn't touching the cam any longer. Then of course when I had throttle, the timing arm advances before the roller touches the cam and adding fuel to motor. I don't get it... I read and re-read the manual to make sure that I understood how to set roller and timing. So why setting timing at 4 deg ATDC if when you advance throttle the timing advances before fuel is added????

Would this explain the shaking?

I would say that the space between roller and cam at idle is about 1.5 mm and that it takes about 7 deg of timing advance before the roller contact the throttle cam. Seems like a lot of advance ???




Anyway, this is where I am and I am in desperate need for help and ideas...

Thank you.

Frederic

 

[tblshur]

could your motor support bushings be worn out

 

[fmt2bx]

could your motor support bushings be worn out

Thanks for the reply. Hard to tell but they are looking ok, I ll try to get a better look.

 

[tblshur]

shake the top of motor back and forth and get hold of bottom and pull up on it see if it has any slack in it

 

[w2much]

link and sync according to the manual.. I am not familiar with your motor but outboards in general I am. The timing usually sets your idle spped. It generally advances before the butterflies open on the carburetor. This is where fuel is being routed through the idle circuit. As the timing advances the roller cam contact begins to open the butterfly valves introducing more fuel. As you throttle up the timing advances and the cam opens the flow of fuel. In setting the linc and sync 1.5 mm seems about right. On my cam there is an outer layer of softer material which surrounds an inner hard plastic. The outer layer dries and breaks off in time so that if you are not familiar with what it looks like you will not be able to set it correctly. In this case the roller cam circumference is decreased therefore it retards the timing. Are you certain your idle speed timimg is set ATDC and your WOT at BTDC ?k
As for the shaking . Is there a safety mode or in OMC language a SLOW mode. This is a feature which prevents the motor from turning fast RPMs when an issue is detected such as hot, oil, ect. Is the motor in a barrel or on a boat ? Is your prop or prop shaft bent ? Are you sure your fully engaged in forward ?

 

[QBhoy]

Without doubt...the most common cause of vibration or shaking at this sort of rpm is the propeller being damaged or even only a tiny bit of damage. All rotational machinery, especially if a tiny bit out of balance have two critical rpm spots that they will vibrate a little. About that rpm and also nearer the top end of things.
perhaps you have ruled this out already, but it’s certainly the obvious cause of such things.