99 Osprey 245 with twin 150 Evinrudes

[Sodcutter]

Hoping to get some feedback on an issue I am having with the starboard engine. While cruising, the engine will start violently shaking, vibrating. Does not quit, just shakes until you throttle back then idles normally. when throttling up, does same thing. After a few minutes at idle it will go on and perform normally. Just does this randomly. Has anyone ever run across this before?

[fitz73222]

Have you noticed any changes in rpm when the engine starts to vibrate? Have you noticed if the engine vibration is sensitive to steering position or it does it start to do this going straight ahead? Crossing a wake? Have you noticed if the vibration is weight shift sensitive? Like if someone walks from one side of the boat to the other? Does this start to happen at a specific rpm? How long has this engine been doing this? Have you made any changes to the boat at all, adding a transducer, adjusted engine toe, trim tab adjustments? New props? Sorry for the barrage of questions. It would be easy to point the finger at an engine problem but this isn't always the case. Try to remember every detail of what's going on when this engine starts to do this. This will sound crazy but try tilting up the port engine out of the water and running the boat only on the starboard engine and yes at wide open throttle or enough to plane the boat and see if she starts to vibrate. It will not hurt the engine. I'm trying to isolate a twin engine set up issue or a engine issue.

[futch13]

Sounds like it's going into S.L.O.W. (RPM reduction).  Is it a 60' 150?  Are you getting  warning horn?  May be fuel vac sensor, temp sensor, oil pump, or may be just bad power pack.

[Sodcutter]

Just bought boat last year and been in process of prepping hull for re gelcoat. Only had it out twice and both times it did this at some point in the trip. Both times in a straight line at around 4000 rpm. Did not continue to run, immediately throttle back to idle. When throttling back up, would go to doing it at much lower rpm, but after few minutes at idle, would go ahead and run normally. Hear no warning horns or lights on the dash. Doesn't appear to reduce rpm's much when this occurs but to keep it from shaking off the back of boat, I reduce rpm's. Have checked plugs and all seem to be ok, all cylinders appear to be oiling correctly. Have not checked compression yet, but that is my next step. Just wondering if there is another possible problem I'm not thinking of. Thanks for any ideas

[Sodcutter]

it is a 60deg 150

[futch13]

Pull the vernatherms (tstats) and see if they have a fin on the block side that goes into a grommet.  This was an old problem where they stuck in the grommet and would not "pop off" when under pressure causing overheat and going into SLOW.  RPM reduction was immediate and would try to throw you thru the console LOL  Motor would also shake and rattle like it was coming off the transom due to spark/timing cutouts.  Should have updated tstats in it by now but you never know.