RPM question- How to increase?

[rooooney]

Sorry If this has been covered already- My 18 ft crest II pontoon has a merc 9.9 on it and it usually runs at 3000 rpm. I think its WOT RPM is 5-6k. For some reason now its running at 2400.

First off, how to I know my RPM gauge is correct?

WHat can I do to increase this?

 

[MH Hawker]

Re: RPM question- How to increase?

Well you need to make sure your tach is reading right, you can pick up a inductive hand held one cheep at harbor freight for 20.00 or less.

and once you know the WOT rpms you can change props to raise the WOT rpms.

Its not uncommon on a 9.9 on a pontoon to be running under the max motor rpm, but you should be able to get it a lot closer. I also am on a 9.9 lake and running a mariner and I have a 9 pitch prop and its tunrning 5200 rpm.

 

[5150abf]

Re: RPM question- How to increase?

Once you figure out the tach then it's time to make sure the engine is running right, a plugged up carb will do the what you are describing also.

 

[rooooney]

Re: RPM question- How to increase?

Carb should be good, I rebuilt it last year. My current full throttle RPM's are about 3800. I can't seen to figure out what the current pitch is. THis looks like a 7 but I'm not sure if that is identifying my pitch?

If it is a 7 should I bump up to a 9 to get some more rpm?

 

[MH Hawker]

Re: RPM question- How to increase?

Wrong direction a 5 P would bring up the rpms, less pitch incresses the rpm`s. the 48- number looks like a merc number that is also a way to find out what it is.

48-42522A12 is a 9 P
48-42521A12 is a 8 P
48-42520A12 is a 7 P
48-42524A12 is a 6 1/2 P
48-42518A11 is a 5 1/5 P