Vibration

[LuckyPenny]

I am trying to track down the cause of a vibration I get from my boat / engine. It only happens between 2150 and 2400 RPM. Above and below that, smooth without any problems. the lower unit is tight, the prop has been checked (sent out and adjusted) the engine mounts are tight. Nothing I check or adjust effects this problem,or changes it in anyway.<br /><br />Any idea's? <br /><br />I am talking about a 1979 100HP Johnson V4

 

[ezeke]

Re: Vibration

You may be over-propped. In other words, too much pitch. <br /><br />If so, you will not find it easy to get near 5,000 RPM, and you may find that easing up on the throttle when accelerating reduces the vibration. You could just try a prop with a lower pitch.<br /><br />There are also about a dozen mechanical possibilities but I don't think that they would be limited to such a narrow range of RPM

 

[ezeke]

Re: Vibration

Back again, Luckypenny, with a PS<br /><br />Here's a site with a chart that may help you find the range of prop that best suits your boat and motor. Just scoll down until you find your motor.<br /><br /> Propeller Chart

 

[LuckyPenny]

Re: Vibration

I don't think it is the prop. It is the same problem with 15" and 17" pitch. It does not matter if I gun it or ease it. I still get vibration.

 

[Forkin' Crazy]

Re: Vibration

It just started doing it? Do you have any loss of power? I have a '79 100 Johnny. Great motors.<br /><br />BTW my 235 V6 Rude vibrates pretty bad at that RPM, but it has solid mounts.... <br /><br />Check that upper mount again. I have seen them go bad deteriorating from the fuel and oil that seeps down from the carbs, etc.<br /><br />FC