Merc/force 120 mods need help.

[Willor]

Any one gone down rabbit hole of trying to squeeze power out of a 99 merc 120hp in-line 4 cyl 2stroke. Well I’m trying and looking for others input and advice. So here it goes Is there a way to gain from porting exhaust ports? Like adding 3 inch to exhaust an adding 3 inch worth of individual diverters or something. I run jet boat so I’m not restrained by an outboard hood. There is a diverter/baffle in there between 2-3. That’s not good enough to allow exhaust porting tho right? Also on porting the ports what about making the 4 round ports into 2 oval ports but not raise timing rather then the squaring the 4 round ports? Also Any recommendations on squish band. Also I need new carbs as well was thinking of going with cpl newer style slide carbs. Last one I Cant find reed stuffers for a 120. How thick are reed stuffers I could mill that amount off intake. Yes I know I’m getting into a temperamental boat but that’s wat I’m into. I know it may not seem it from all the questions but this is huge platform and maybe get the right gear heads like myself

 

[jerryjerry05]

What's a reed stuffer???

Look up all the posts by FrankA. Frank Amphora he did a lot of mods to these Force and Chrysler outboards.
Look for his u-tube video's too.
He did posts on porting and polishing and boring.
IF?? my memories right(maybe? maybe not?)
The 99. It was originally a 125 measured at the crank???
Then in 89/90 they changed to a 120 and the 85 went up to a 90hp.
That year they standardized the lower units by using the same gear ratio on all the motors,90/120/150
After a few years they stopped production on the 150.
That motor actually ran pretty good. They said it was the best power to weight ratio of all the outboards,OMC Merc,and Yam included.
Early 90's they started messing with compression #s. The 120 had different
pressures on #1/4 than #2/3 10-20# difference on the cyl.
FrankA really knew his stuff.
He passed to young.

 

[racerone]

Reed stuffer.======A means to reduce crankcase volume.-----Done to get higher crankcase compression.-----Done to get better and more complete scavenging of cylinders.----Used on some Johnson / Evinrude 135 / 140 HP models back in the 1970's