Need to limit RPM's

[mustang sally]

Hi everyone,
I have a number of new 250 3.3 l engines I use in a charter/ferry application. I would like to limit the max RPM to 4500 so my captains will not drive them to hard. Can anyone tell me how to do this. I know on old 2 strokes there was a screw on the engine but not sure about 4 strokes. I am guessing there is a way to do this either on the engine or the throttle handles. I do not want to change props.

[boscoe99]

What kind of control box are you using with the motors? Top mount 704 box or side mount 703 box?

You are correct about the propellers. Prop the motor so that it can reach at or near 6000 RPM with the boat loaded. Then, some how, some way, either physically prevent the throttles from being opened beyond 4500 RPM or better educate the drivers. You can check up on them via YDIS.

[mustang sally]

704's on our twins and the standard yamaha triple lever on our 3 engine applications.

[boscoe99]

The 704 box has a forward and reverse limit function. Not sure if it will be enough to prevent the throttle from going further forward than 4500 RPM. You will have to test the box as it is configured today to find out.

If the forward limit is not enough perhaps you can find a screw that is longer than the existing screw and install it. It might have to be a trim-to-length operation until you find what works best for you.

Keep in mind that if the throttle is restricted then it might effect the boats ability to get onto plane in a reasonable time frame. I would suggest that you reinforce your desires with your crews and then monitor their operational pattern via YDIS as opposed to limiting the throttle movement. Up to you however.

[donsmarine]

Put a block in front of handle after propping correctly which prevents full throttle advance?

[robert graham]

Put a block in front of handle after propping correctly which prevents full throttle advance?

Sounds like a nice simple solution....assuming your captains just will not respect your order for 4500 RPM maximum!....

[DennisG01]

Like Boscoe mentioned, I would have reservations about physically limiting the travel of the throttle stick. Whether for trying to get on plane with a heavy load, or a possible emergency situation. However, if there was a way to electronically limit the RPM's, that might be a safer choice. Although, that's not to say that I know of a way. Ultimately, I think the best situation - as noted above - are competent, reliable and trustworthy captains. And if you feel the need, monitor the engine performance with a scanner. If you feel that guys you have working for you can't be trusted, it might be time to find some new guys.

[99yam40]

Like Boscoe mentioned, I would have reservations about physically limiting the travel of the throttle stick. Whether for trying to get on plane with a heavy load, or a possible emergency situation. However, if there was a way to electronically limit the RPM's, that might be a safer choice. Although, that's not to say that I know of a way. Ultimately, I think the best situation - as noted above - are competent, reliable and trustworthy captains. And if you feel the need, monitor the engine performance with a scanner. If you feel that guys you have working for you can't be trusted, it might be time to find some new guys.

nicely worded and the best solution in my opinion.
You will be lugging a motor for a long period of time trying to get up on plane by limiting the throttle movement, if it will even get up on plane with that limitation.

4 strokes need to run at the higher RPMs to keep running properly