Nissan/Tohatsu 9.9 two stroke upgrade(I wanna make it fast)

Picked up this old Nissan 9.9 Two Stroke today. Another Craigs List treasure. Motor runs great as is, but the local restriction on the lake I fish is 10hp. I've heard of being able to soup the old Nissan/Tohatsu 9.9 two stroke motors up to a 15 or 18hp. I wont lie, I'm trying to be the fastest guy on the water. One of the guys I fish against has made it personal, and I gotta be faster than him. I've got a set of High Performance Boyesen Reeds to install and I'm looking to do whatever else I can to make it faster/stronger. It's going on a G3 1448. Any Ideas? Better Plugs? Different Prop? Carb Change? Thanks, any advice is greatly appreciated.

I forgot to mention, the motor is a 1992, model # NS9.9B2 Short shaft manual start. Thanks again.

I'm not sure what you can do to the motor,,,maybe new carb,reeds,without going to crazy.
Some people run their outboards over the recommended rpm's,probably shorten the life of the outboard.
Different props can change the speed,2/3/4,etc. blade,rake,cup,thrusting,thin the props out,change to stainless.
Position of outboard in water,jack plate.
Lighten the boat.
May want to find a small outboard racing forum.

i know this motor well.. my father in law had one and my friend ronnie had one as well.. that is one reason why i bought a 09 tohatsu 9.8. but anyway, there is a set screw in the throttle you can remove to make it a 15hp. its the same motor just the 9.9 has a throttle limit on it ..I think he runs with a 8p prop too.. the skiff scoots up the lake..

i have not done this mod, but that is what I was told about it....

The Nissan-Tohatsu 9.9 and 18 hp are two seperate blocks with different displacement. At least the 2000 models were, I checked when I bough my 18 Nissan.

tohatsu 9.8. but anyway, there is a set screw in the throttle you can remove to make it a 15hp

Click to expand...

you will get some more throttle out of it, but you will not gain 5 hp out of it on such a small motor

to make power the motors gotta breath. thats always the first place to start. port/polish the intake exhaust and i'd even polish the crank. after that you want more fuel (change carb jets). once thats working i'd start playing with high octane and timing. generally the slower burn you have (higher octane) you'd need to retard the timing a hair. theres really no rule of thumb you just have to play with it untill its right

thats alot of work to get into though, may just want to find a prop that will give you more top end

Loggerhead Mike said:

to make power the motors gotta breath. thats always the first place to start. port/polish the intake exhaust and i'd even polish the crank. after that you want more fuel (change carb jets). once thats working i'd start playing with high octane and timing. generally the slower burn you have (higher octane) you'd need to retard the timing a hair. theres really no rule of thumb you just have to play with it untill its right

thats alot of work to get into though, may just want to find a prop that will give you more top end

Click to expand...

Keep in mind that all this (short of swapping props) will shorten the life of the engine. It was not designed to have much more fuel/air poured into it, or power poured out of it than the OE carb jets and all would allow. If you look into the performance outboard world, there are very few old outboards being used, and the ones that are used are ones that have very few hours on them since being hot rodded. Your motor was designed to be a long lasting reliable runner, not a performance race engine.

More Air in means more fuel in which makes more power. Bigger Carb and intake ports are a must on N/A engines. On top of that, Porting requires not really bigger but better flow. You can gouge out the intake port and actually do more damage to the cfm than you do good. Two stroke engines also require back pressure on the exhaust side to keep the engine happy. So with the increase in air / fuel in, you will have to do some work on the exhaust system but like i said, with two strokes, it is tricky. I would stay away from higher octain fuels. Going to higher octain will actually slow the motor down. Fuel doesnt not burn completely with you run too high octain on lower compression engine. Stick with what the manf sugguest or maybe two points higher at the most. I do not have tons of experience with Two Stroke Engines but i do build the engines for our 2 Super Comp Dragsters =)

This thread has just been SPAMMED . . . by a 1 post wonder.

I've had two 9.9 Mercs ('02 and '04). Complete carb replacement to the 15hp carb made them both really come alive. I'm not familiar with nissan but I would think carbs would be different as well. (maybe not)?

One absolute sure way to make that little motor faster is to put it on a lighter boat. One of my Mercs was on an all welded 1448 and the other on a riveted 1436. The 1436 would run circles around the 1448. If your serious about being the fastest boat on the water you need to be one of the lightest boats on the water.

[url=https://www.tinboats.net/forum/viewtopic.php?p=96804#p96804 said:

bassboy1 » 06 Jul 2009, 14:10[/url]"]

Loggerhead Mike said:

to make power the motors gotta breath. thats always the first place to start. port/polish the intake exhaust and i'd even polish the crank. after that you want more fuel (change carb jets). once thats working i'd start playing with high octane and timing. generally the slower burn you have (higher octane) you'd need to retard the timing a hair. theres really no rule of thumb you just have to play with it untill its right

thats alot of work to get into though, may just want to find a prop that will give you more top end

Click to expand...

Keep in mind that all this (short of swapping props) will shorten the life of the engine. It was not designed to have much more fuel/air poured into it, or power poured out of it than the OE carb jets and all would allow. If you look into the performance outboard world, there are very few old outboards being used, and the ones that are used are ones that have very few hours on them since being hot rodded. Your motor was designed to be a long lasting reliable runner, not a performance race engine.

Click to expand...

i disagree....a 9.9 2 stroke is basically a "detuned" 15...if you change the carb to the 15 carb, and bump the timing, its not really hot rodded...itll be a 15...

if im not mistaken, i do think theres an exaust port you have to open up also...

i can put you in touch that has done several of these....

Loggerhead Mike said:

i disagree....a 9.9 2 stroke is basically a "detuned" 15...if you change the carb to the 15 carb, and bump the timing, its not really hot rodded...itll be a 15...

if im not mistaken, i do think theres an exaust port you have to open up also...

i can put you in touch that has done several of these....

Click to expand...

I have a friend who used to do this - bump up the output. He said much the same things.