Maximum RPM?

[jimyoung]

My 1988 merc 115 hp is only reaching approx 3800 rpm....it is on a 28 foot pontoon...runs fine otherwise ideas?

 

[WillyBWright]

Re: Maximum RPM?

Are you absolutely certain that it's running on all six? What have you done to check? What is the pitch of your prop? I'm thinking you want a 13.

 

[jimyoung]

Re: Maximum RPM?

It runs to good,(except rpm) to not be running on all six, starts good, idel may be a lttle low, but runs fine...a "13" ? this is prop dia?

 

[Droll]

Re: Maximum RPM?

**
...a "13" ? this is prop dia?

Propeller pitch, the theoretical distance a propeller will move the boat forward on one revolution .

Usually propeller are marked with "diameter X pitch" ( like 13" x 13" ).

Arne Kjetil

 

[studlymandingo]

Re: Maximum RPM?

Check your spark, this is what WBW is suggesting. Get a spark-gap tester at an auto parts store (they are very inexpensive) or use an inductive timing light.

You may have to remove the prop to get the numbers off of it, they are often times located on the hub. If the spark is fine and fuel delivery is adequate, then you may be over-propped; if this is the case, you need to reduce the pitch.​

 

[jimyoung]

Re: Maximum RPM?

Thanks for the suggestions.........I will check her out.