Whaler Central - Boston Whaler Boat Information and Photos

Posted by mikewarner on 09/10/09 - 6:45 AM

I e a 1989 70HP Yamaha Engine on my 15ft SS. I am getting alot of engine vibration at idle speed. Do you think that this could be caused by a bad spark plug?

Posted by jaxmyth on 09/10/09 - 7:47 AM

i have an 88 yamaha 70 and i'm experiencing the same thing. please someone help. prop is good.

Posted by Derwd24 on 09/10/09 - 7:51 AM

Do you mean idle speed in gear with the boat moving, or idle speed in neutral with the engine just idling?

Posted by joninnj on 09/10/09 - 8:39 AM

If it idles smoothly in neutral but not with a load, that could mean a few things. I would start with the prop, maybe not balanced or has a bent blade, the prop shaft may also have be slight bend... I would also look at the fluid in the lower unit, if the shaft is bent the bearing will get damaged and water may seep in.

Also do a basic compression check, slightly low readings could effect how it will idle under load.

Could also be something simple like a fuel delivery issue...

Does it seem to run fine at high speeds?

Posted by moose on 09/11/09 - 10:33 AM

All my old outboards would spit and sputter on startup, especially when cold. The engine would jump all over the place when it missed, coughed, or sputtered. Is that what you mean, or is it a steady vibration that is rpm related?
Mike

Posted by Eri on 09/12/09 - 7:34 PM

Most two strokes shake as they get old depending on the hours used. The SHAKES all my boys call it. It could be caused by bad plug. It could also be caused by a carb idle circuit being clogged. Compression check good place to start if the plugs all look good.

Posted by Derwd24 on 09/12/09 - 11:38 PM

Did this come on all of a sudden or has it been gradually getting worse?

Would also add to the above to check the rubber motor mounts as another possible cause.

Posted by MW on 09/13/09 - 12:12 AM

What cond. and how old is the prop ? I've severely damaged props in the past with no visable or noticeable difference in it's performance, I've also slightly nicked/damaged them where they look o.k. but, performance is clearly suffering by a "Ventilating" prop., replacement was needed. It's also been my observation that 2- stroke motor's prefer to be up at higher RPM's, and don't like to run slow (idle) speed, They're hard to "Balance", that's why you don't see "V-4" automotive engines.

Posted by number9 on 09/14/09 - 8:19 AM

#10

From a 2000 P60-C90 Service Manual, Trouble Analysis Chart, Rough Idle. Does not differentiate between neutral and in gear. Also do not believe it is any type of suggested order for trouble shooting. As others have suggested trying a known good prop would be a good starting point.

Fuel pump.
Link adjustment.
Compression.
Reed valve.
Cylinder head gasket.
Ignition coil.
Spark plug cap.
CDI unit.