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I finally took my "new to me" 1972 16'7" whaler out after the winter on a local lake. It has a 1992 88HP Johnson. After a quick warm up, I took it at almost wide open throttle and it moves really nice and very fast. The thing I'm concerned with is, as I slowed it down I noticed a slight, constant shake while sitting in the boat at lower RPM's. If I stood up I really couldn't notice it. The only other boat I have owned is a 14' center console with a 15 HP four stroke which was really smooth so I'm wondering if this is a normal 2 stroke thing or should I investigate it further? It had a brand new prop installed before I bought it.
Thanks
Steve

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Many motors have a "rough running" window at slower speeds. You'll probably find that it does it at a certain RPM range and other times you can't even notice it. That may or may not be what occuring on yours, but that is the case with many motors this is somewhat normal.

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To clarify:

When not moving, with the engine idling, you saw the engine shaking a bit? Do you know what RPM it does this consistently?

My Yamaha 90 had a rough area right before the boat would get up on a plane. I got used to it. If I was motoring slowly, I would just avoid that rpm.

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Steve

Congrats on the new boat. Where in MA are you?

I had that same engine on my Montauk (slightly older, it was a 1988 88 hp). Plenty of power for that boat, and a fairly bullet proof engine. I have nothing but good things to say about it.

I bought the boat used, and the engine had lots of hours on it already. I put a lot of hard hours on it over a ten year period, and it still ran great when I sold it.

I did have a similar situation on my boat one year. I hit a rock at speed & ruined my prop. After replacing it, I had a noticable vibration at low speeds. Turned out that I had slightly bent my output shaft on the lower unit. My mechanic that diagnosed it told me that it would be fine as long as the shaft seal did not fail & let water into the lower unit.

I ran it well over a hunded hours that season; I just regularly checked my lower end oil to make sure it wasn't contaminated with water. My mechanic replaced it in the fall after the season was over. I would have to dig thru my old paperwork, but I don't recall it being that expensive a repair.

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Thanks for the info guys.
I am wondering if the prop was changed because of the similar situation flippa had.
When I get some time, I'll remove the prop and check the runout with a dial indicator. I just bought a service manual on ebay and the spec should be in there.
I'll keep an eye on the oil too.

Flippa- I'm in Upton-basically the junction of the Pike and 495. Are you "in" Boston?

Steve