1987 J120 VRO W.O.T RPM range question.

[kbmsound]

Hi all. I have an 87 Johnson 120, model J120TLCUR and was wondering: What should be the rpm at wot in this motor? Ever since I got it I have not ran it past 4500 rpm due to not knowing what the max safe rpm are for this specific motor. Also, I would like to know if anyone has any tips to safely increasing HP on it. I have heard that swapping out carbs is an option. I just want to get a bit more top speed out of it. I think swapping the prop is also another route? Thanks in advance.
Les.

 

[interalian]

Safe to at least 5500rpm

 

[marauder11]

I am no motor head but i believe you would need to bore the motor out to get bigger pistons in it for more HP.

I had the same motor they are great.

You may be able to mind info for you motor here too
http://boatinfo.no/lib/library.html

 

[Bosunsmate]

Yes another prop would get you more top end speed, the pitch number has to be larger than your current one.
That would reduce your lower end pulling power for skiing etc though

 

[emdsapmgr]

According to the factory sales brochure, a 120 has a normal operating range of 5000-6000 rpm's. Current thinking is that you should prop to run in the upper end of the "normal" rpm range, or 6000 rpm's. Anything under 5700/5800 and the engine is considered "lugging".

 

[Faztbullet]

I am no motor head but i believe you would need to bore the motor out to get bigger pistons in it for more HP.

Boring does not add HP......

, I would like to know if anyone has any tips to safely increasing HP on it. I have heard that swapping out carbs is an option

Swap the intake,throttle bodies and carbs off a 140hp. This is the small bore 2.7 bridged port motor and cooling is critical for it to live.

 

[kbmsound]

Boring does not add HP......

Swap the intake,throttle bodies and carbs off a 140hp. This is the small bore 2.7 bridged port motor and cooling is critical for it to live.

Thanks FaztBullet, that is what I thought about doing.

 

[sutor623]

You haven't even opened the throttle past 4500 yet and are looking for more HP? Open that girl up and see what she can do first!!!