Boat revs out

[LarryFine]

My boat mechanic said that my boat revs out at 5500 rpm which he said was a bit low. What does that mean?

[noelm]

For best performance the motor should be capable of achieving manufacturers max RPM with a normal load. Max RPM too low will cause more fuel use and shorten engine life, being able to reach max RPM doesn't mean you have to run it there but, it must be able to get that RPM

[noelm]

Just to add, a few things affect RPM, motor too low on transom, prop too big, trim not set right, what motor do you have? Is this a new rig or new to you?

Edited March 31, 2022 by noelm
Typo

[frankS]

First up check your prop size. ( sounds like your prop may be too big )  make sure the throttle cable is opening carb's all the way, A number of things that could be the problem but these 2 would be the likely cause.

I'm surprised your mechanic hasn't told you of these possible causes.

Frank

Edited March 31, 2022 by frankS

[noelm]

Just to explain, this is especially for carby 2 strokes, what happens is, the timing advance is a fixed linkage, joined to the throttle, when you push the throttle down, it advances the timing, no way around it, if your RPMs are low compared to the throttle opening, the timing is way too advanced! Why is this bad you ask? In simple terms, the piston is coming up the cylinder, before it gets to where it should be, the spark fires, burning the fuel mix and tries to push the piston backwards down the cylinder, but the other cylinders keep it going up, causing excess heat, and then "detonation" which will just melt your piston, which is not a good thing. Too big a propellor causes you to have to open the throttle more than necessary, that sets the whole situation above in motion, plus the extra throttle increases fuel use for no benefit. Just to note, if you ever have to tow someone in, take it slow, do not go at high power, but only slow speed, regardless of what type of engine you have.

Edited March 31, 2022 by noelm
Added something

[dunc333]

great explanation nolem makes sense 

[Fab1]

Just be like me.Mine revs out at 0 rpm sitting in garage and every week I look at it it hasn't used any fuel at all.Very fuel efficient.

  Great advice both Frank and Noelm have given you.

[noelm]

That's why I asked what motor he has, but it appears he has vanished.

[LarryFine]

115 hp mercury

 

[noelm]

What model, 2 stroke or 4 stroke, brand new, new to you?

Edited April 2, 2022 by noelm

[dunc333]

 i get engine height right  first ,then play with prop pitch cheers dunc 333

[noelm]

Yep, height first, always, a motor too low will drag RPM and performance down, and fuel use up.