Yamaha 25 hp 4 stroke vibration

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G3 JON

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recently mounted a 2006 25 hp Yamaha 4 strike to my G3 I had a 25 Mercury 2 stoke mounted previously. After running the Yamaha a few times had to get mechanic to clean carb due to mid range power loss. Engine runs good now just seems to have more vibration than my Mercury did even rattles my boat paddle loss from its mounts some times. The Yamaha dealer says seems to be normal anyone else have one that can give me some feedback
 
If it vibrates all the time wide-open throttle and at idle then maybe your prop shaft is out of balance our bent. If it only does it at idle then possibly your rpm's at Idol or set too low.


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hard to say without running it, but at certain engine speeds, they do vibrate a little. Reason being, it's a parallel twin cylinder with a 360 degree crankshaft, meaning both pistons move the exact same direction at all times. This design MUST use a counterbalancer of some sort, and Yamaha thought it was best to use a big heavy slug on the opposite end of the pistons. All of the 4 stroke twin cylinder outboards are the same way, except the old suzuki which was a VERY disappointing V-twin design. The counterbalancer helps but it won't stop the vibration at certain speeds, specifically lower speeds, right around 1400 RPM, then again at about 1700-1800. After that it goes away. I have one of those motors and I hated it at first, but you get used to it. I moved a few things around in the boat so that the wouldn't rattle so much. It sure beats drowning in your own smoke and having to mix gas and oil.

The only suggestion I have is to make sure the fuel that's in the carb gets either drained or used often; as those passages inside the carb are tiny, and plug easily. On mine, if the fuel is more than a couple weeks old, I notice a little rougher running....actually a month or so ago, the motor would just fall on it's face out of the blue. Ran home and got my other 3 gal tank and put fresh fuel in it, problem solved. Weird.
 

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