What are the symptoms of underpropped motor?

[496 Cubic Inches]

I have a 2004 Yamaha 50HP with oil-injection. The last few times I've had my boat out by myself I've noticed it's running weird at WOT. It runs great at all speeds up to WOT,then it gets a weird vibration and sounds like its not running right. Almost like its bouncing off a rev limiter. I don't have a tach yet so I can't confirm its running too many RPMs. <br /><br />Its got fresh gas,properly gapped new plugs,ect. <br /><br />The only thing I can think of is that I usually have two other guys with me and its keeping the RPMs and speed down a bit. When I'm by myself I've gained about 5-6 MPH and thats raising the RPMs as well.<br /><br />any ideas?

 

[Ray Neudecker]

Re: What are the symptoms of underpropped motor?

Without a tach, you can do nothing but guess.

 

[Grant S]

Re: What are the symptoms of underpropped motor?

Do you know anybody with a coarser prop you can borrow to try?

 

[Fully_Loaded1]

Re: What are the symptoms of underpropped motor?

The rev limiter will make it sound like the motor is missing, but like Ray said without a tach your dead in the water. They are easy to hook up and I would recommend one.

 

[twnichols]

Re: What are the symptoms of underpropped motor?

I have 2004 50 4 stroke yammi. Can anyone recommend a tach other than yamaha's multitach, they are high dollar $250...ouch. 496 what pitch are you running on your prop?