Is it possible to exceed maximum rated RPMs?

[eavega]

I have an FD-22 (20 HP Johnson) that is just about ready for its second test run on the back of my boat. I had a question about an observation I had on the water; is it possible for a motor to exceed its maximum rated RPM? I have a tiny-tach installed on the motor, and it was reading about 6800 RPM when I ran WOT. The specification of this motor states that full throttle operating range is 4000 to 5000 RPM. Should I be looking at the tiny-tach as the culprit of these high readings, or is this motor really rotating 1800 RPM above its operating range?

 

[F_R]

Re: Is it possible to exceed maximum rated RPMs?

Heck yes it is possible. Is it really revving that high or is it the tach? I have no idea.

What boat do you have it on and what propeller do you have? Those items (along with load) determine what your max RPM will be.

You sure don't want to be running it a 6800. It is a tough motor, but even tough has it's limits.

 

[kenmyfam]

Re: Is it possible to exceed maximum rated RPMs?

It is very easy to over rev. It is set by your load being pushed along and set up. Could be well under propped. You need to verify the tach is correct or not though before jumping to any conclusions.

 

[Dhadley]

Re: Is it possible to exceed maximum rated RPMs?

It's very doubtful that motor will breathe well enough to get that kind of rpm with stock reeds & port timing. Check the tach to make sure it's the correct one for your application.