maximum rpm

[strokersquid]

I just bought an Arima 17' boat powered by a 100 HP 1993 Merc 2 st. The boat maxes out at 4500 rpm, though I have no speedo to say how many mph that is. What is the recommended max rpm range for this motor, and what is the usual rpm range for cruising ?

 

[oldman570]

Re: maximum rpm

According to "1manual,com" max operating range for it is 5250RPM best range starts at 4750RPM. Spec sheet can be found along with compleat info for the motor there.
Oldman570

 

[strokersquid]

Re: maximum rpm

thanks

 

[Alumarine]

Re: maximum rpm

You are over propped. You need to get a prop that will allow the motor to rev at the max rpm range.

You will probably use less fuel as well as the motor lasting longer.

 

[strokersquid]

Re: maximum rpm

that had occurred to me. I will have to check if it maxes at 4500 ( too low ) or if it really is more like 4750, which would be ok.

 

[Silvertip]

Re: maximum rpm

that had occurred to me. I will have to check if it maxes at 4500 ( too low ) or if it really is more like 4750, which would be ok.

4750 is still too low. That's at the bottom of the range. If you add a couple folks the engine will be lugging. Two strokes don't like that.

 

[strokersquid]

Re: maximum rpm

that number was with 2 adults and 2 100 lb children, though thats the usual load so I may indeed need to "de-prop"

 

[1nebel0]

Re: maximum rpm

You need to step down at least two sizes in prop.. If you are running a 19 then go to a 17...17 go to a 15 at the least.. you want to me at the max side of the motor...these motors don't mind being revved up but will not forgive you being lugged...you are looking at buying a new motor in no time..........

 

[strokersquid]

Re: maximum rpm

this is the original engine and prop a/t the previous owner. That would mean it's benn this way almost 20 years now

 

[phebus1]

Re: maximum rpm

Boats are commonly sold with the "wrong" prop for the customers application. Are you running the boat at altitude, is the motor mounted at the proper height, are you running with a load (anchor, coolers, extra battery, etc). All these come into play when selecting the proper prop. Now, add the fact hat it is a 20 year old motor and probably doesn't have the power it originally had, and the prop probably isn't in pristine condition and you find yourself with an over propped condition.
Bottom line is that you need to prop for your current conditions, but I would only do so after tuning the motor to make sure it was delivering what it could.

 

[Texasmark]

Re: maximum rpm

this is the original engine and prop a/t the previous owner. That would mean it's benn this way almost 20 years now

He could have been running at a lower altitude, or a lighter load. If not or regardless, get yourself a few cans of Sea Foam and run them in your gas tank along with the normal fuel/oil ratio. Directions are on the can....auto parts store, ww. It will clean up your combustion chambers/exhaust that are probably all gooed up if in fact the engine was lugged for all those years.

Mark

 

[Texasmark]

Re: maximum rpm

Boats are commonly sold with the "wrong" prop for the customers application.

I bought a new Ranger BB with a 115 tower and the dealer had a 24P prop installed. Same thing. Apparently he didn't have any SS props in his inventory for that engine....he apparently had props for 150 xr(whatever) that could swing that much pitch. I had to drop down to a 21 to get where I wanted in rpm's which was 6000 even though max range was 5500. Engine loved the rpm's....used to sing like a bird and since I ran the prop partially out of the water, you could hear the blades hitting the surface making a humming noise. Music to my ears.

Mark