2005 115 optimax "beeping" then powering down?

Question

I just changed props on the engine because I was not happy with the hole shot, I went to a trophy plus four blade SS 17 pitch prop, this was what was recommended based on the mercury propeller selector, and confirmed this with the guy at the parts counter where I ordered the prop. I was running a laser II 20 pitch, rpms at top speed was 5200, with the new prop I am much better out of the hole and about 5 mph faster, but at top speed I am hitting 5900 rpm and then sometimes my gauges make a beeping noise and the engine powers down to about half power and the rpms go down to about 4000. Why is it doing this, are my rpms too high and the engine is powering down to avoid damage? What is the max rpm this engine can handle. All help is appreciatted.

Answer 1

The optimax has a gaurdian mode. You are exceeding the RPM limit of 5750-5800. The guardian mode powers down the engine so it won't damge itself.  I would try a 19 trophy plus or a 19P laser.  A lot of times before you buy a prop a dealer may let you try it out to see if its the right prop for you. I would ask to demo the above mentioned props and see which works the best for you. Hopefully you can trade in your still new prop for no extra money to get the one that works best.

Answer 2

Your rev limiter is coming in to many RPMs send the prop out have more cup installed it will drop it down to 5600 to 5700

Answer 3

That's your overspeed alarm  on the guardian system, telling you that you are overrevving the motor.  When you reach a certain rpm over the redline, the shuts down cylinders to protect itself.  Neat, eh? You need to get a prop with more pitch.  That 20 inch, where you where running at 5200 is not bad. 5200- 5750 is recommended WOT, and keep in mind that most marine tachs have a variance(unless you have Smartcraft).  Continous overspeeding WILL damage the motor.

Answer 4

The prop is reving up about 4 to 500 rpm's too much- that is the rev limiter kicking in and protecting your motor from blowing up- you are lucky your motor had this on it.

Answer 5

It may well be or could be causing it overheat and power down