Low RPM on a new outboard...All suggestions welcome

[Ken Kitchen]

The original outboard on my 18' pontoon died 2 years ago, (1999 60hp bigfoot 2-stroke). I replaced it with a new Mercury 60hp Command Thrust 4-stroke. I did baby it for the first season, now it's showing 26 hours so I'm thinking I should be able to run it WOT.
My problem is: I can't get over 4k rpm. I still have half the throttle to go but no more rpm/speed?
I keep it on the water during the season so working on it is nearly impossible.
Any suggestions ??

 

[racerone]

Was the correct propeller installed?------

 

[QBhoy]

As above for sure. All too often, quite common and absolutely wrong to assume that the prop from a previous engine, should be just fine on a new engine. Even if the same apparent HP. Haven’t looked it up or haven’t even an incline for sure…but there is a high chance that not only the rpm range between these two engines probably differ..but also very likely that the gear ratios certainly do.

 

[Scott Danforth]

The original outboard on my 18' pontoon died 2 years ago, (1999 60hp bigfoot 2-stroke). I replaced it with a new Mercury 60hp Command Thrust 4-stroke. I did baby it for the first season, now it's showing 26 hours so I'm thinking I should be able to run it WOT.
My problem is: I can't get over 4k rpm. I still have half the throttle to go but no more rpm/speed?
I keep it on the water during the season so working on it is nearly impossible.
Any suggestions ??

You are over propped and possibly too deep

 

[Ken Kitchen]

You are over propped and possibly too deep

I have a 13 pitch prop on now... think I should go down to 12 or 11 ?

 

[Ken Kitchen]

Was the correct propeller installed?------

Same prop as the older outboard

 

[brodmann]

Not unless the old motor was the same HP, same WOT range, same weight, height and ............

 

[jlh3rd]

If a new 60 hp CT gearcase diameter is bigger than a 24 year old bigfoot gearcase, the old prop won't work. It will ventilate due to exhaust gas around the prop.

 

[Scott Danforth]

If it was ventilating, the motor would hit the rev limiter

 

[JohnSz]

-Make sure the bore sleeve was installed.

-Engine might be in guardian mode.

-Was the tach setting changed with the new 4-stroke?

 

[Mudtim]

The original outboard on my 18' pontoon died 2 years ago, (1999 60hp bigfoot 2-stroke). I replaced it with a new Mercury 60hp Command Thrust 4-stroke. I did baby it for the first season, now it's showing 26 hours so I'm thinking I should be able to run it WOT.
My problem is: I can't get over 4k rpm. I still have half the throttle to go but no more rpm/speed?
I keep it on the water during the season so working on it is nearly impossible.
Any suggestions ??

Check the control cables at the engine. Open the throttle full not running. You have adjustable cables for forward and reverse there. Have assistance to identify the forward cable. Then adjust accordingly. Not to go past max RPM of motor. Has this vessel been recently repowered?

 

[jimmbo]

The original outboard on my 18' pontoon died 2 years ago, (1999 60hp bigfoot 2-stroke). I replaced it with a new Mercury 60hp Command Thrust 4-stroke. I did baby it for the first season, now it's showing 26 hours so I'm thinking I should be able to run it WOT.
My problem is: I can't get over 4k rpm. I still have half the throttle to go but no more rpm/speed?
I keep it on the water during the season so working on it is nearly impossible.
Any suggestions ??

Babying it, isn't a good way to break in an Engine. Bursts of WOT are needed, to properly seat the Rings. Who did the Rigging? If a Dealer. hopefully the Rigger was competent enough to reset the Tach if need be. Same should have happened regarding the Prop Choice.
As pointed out above, different Engine likely have different RPM ranges, different Gear Ratios, and possibly even different Prop Hub Diameters.
If the engine is hitting and staying at a RPM, and you haven't got the Throttle all the way open yet, it could be on the Rev Limiter, which would mean, either too little Pitch, or the Prop is ventilating, likely from Exhaust getting into the Blades, but it could be air from above the Water

 

[JohnSz]

Babying it, isn't a good way to break in an Engine. Bursts of WOT are needed, to properly seat the Rings.

The Merc operations manual would have had the break-in procedure. On my new 150, for the first few hours, had to go to wot for a minute, every 10 or so. Hope that isn't the OPs problem.