Can you change a Tohatsu 9.9 hp to 20 hp?

[BobGlover]

I’ve got a 3 yr old Tohatsu 9.9 hp outboard, and would like to get more speed. I’ve heard that a simple carb change can increase the motor to 20 hp. Is this correct? If so, about how much speed increase would I get on my 16 ft. flat bottom? Now, it goes about 12 mph tops When I’m alone.

 

[Scott Danforth]

In 3 easy steps

1. Sell 9.9 for small pile of cash
2. Empty wallet into pile to make it bigger.
3. Take bigger pile of cash and buy 20hp

 

[aspeck]

If you are getting 12mph with a 9.9, a 20 will probably get you about 16mph, maybe a little more. But no, you aren't going to turn you 9.9 into a 20 in cheap and easy steps. The best way is as Scott said, sell the 9.9 and buy a 20.

 

[km1125]

I think you can get the 9.9 up to 15 with a carb change. On the older 9.9 you could go to 15 with just the carb change, or up to 18 if you also did the cam.

Does your boat get up on plane at 12MPH? If not, then the 15 might get you up on plane which would increase speed quite a bit. If you're already up on plane then you might just get a few MPH.

 

[tpenfield]

I’ve got a 3 yr old Tohatsu 9.9 hp outboard, and would like to get more speed. I’ve heard that a simple carb change can increase the motor to 20 hp. Is this correct? If so, about how much speed increase would I get on my 16 ft. flat bottom? Now, it goes about 12 mph tops When I’m alone.

Might just be Internet hearsay about the HP increase . . .

Often motor models that are a small HP increment from each other are done with carburetors/throttle settings. I have seen this in a variety of small motors, not just outboards. I would think the 20 HP model is all together a larger powerhead.

Maybe you will get 18+ mph out of a 20 HP, . . . hard to tell, but a flat bottom boat is likely to get up on plane pretty well.

Scott has the right advice . . . there is value in the current motor. Turn that into cash and look for a reasonable deal on a 20 HP.

 

[pvanv]

The 9.9/15/20 E are all identical blocks. I assume that is your model. EFI difference is in the air restrictor and ECU. You need to change both. Price about $1K. Better to sell and then buy the model you want.

 

[BobGlover]

The 9.9/15/20 E are all identical blocks. I assume that is your model. EFI difference is in the air restrictor and ECU. You need to change both. Price about $1K. Better to sell and then buy the model you want.

Reason I don’t want to sell is that the majority of my fishing is on a 9.9 hp restricted lake. I want to fish other, non hp restricted lakes. The 20 hp would allow me to do this.

 

[tpenfield]

Reason I don’t want to sell is that the majority of my fishing is on a 9.9 hp restricted lake. I want to fish other, non hp restricted lakes. The 20 hp would allow me to do this.

Understood- it does look to be the same powerhead. Not sure the upgrade is all that feasible. Maybe get the 20 and get a decal set for the 9.9

 

[Scott Danforth]

Most of my best times fishing were plowing with an old Gale 12hp.... Not getting anywhere fast.

 

[MattFL]

Most of my best times fishing were plowing with an old Gale 12hp.... Not getting anywhere fast.

We had some childhood fun with an old Firestone, the kind you wrap the rope around the top to start it. I'm not sure what horsepower it was, I'm going to guess 2-3HP range.

 

[km1125]

I thought the OP had a carb'd motor?

 

[MattFL]

Look up your motor and the same year 20HP on a site like Partzilla and start going through the usually suspects one by one looking for differences in part numbers. Carburetor, intake manifold, ECU, etc.. If you can get a handful that are different, then start figuring out the differences and maybe you can make an educated guess as to which parts you would need to change. Also verify that the long block and head are the same part numbers, just to be sure they really are the same motor.

 

[BobGlover]

I was surfing the ‘net and the website www.readysetboat.com has a kit that they claim converts the 9.9 Tohatsu to a 20 hp. It consists of a carburetor and a propellor. They don’t say anything about changing the ecu or restrictor plate. Is this legit?

 

[MattFL]

I was surfing the ‘net and the website www.readysetboat.com has a kit that they claim converts the 9.9 Tohatsu to a 20 hp. It consists of a carburetor and a propellor. They don’t say anything about changing the ecu or restrictor plate. Is this legit?

See if you can find anyone who has used it. Also make sure it's all OEM parts, ask the person who is selling the kit if it's OEM or aftermarket parts.

 

[Scott Danforth]

I was surfing the ‘net and the website www.readysetboat.com has a kit that they claim converts the 9.9 Tohatsu to a 20 hp. It consists of a carburetor and a propellor. They don’t say anything about changing the ecu or restrictor plate. Is this legit?

Most likely not

There is no magic bullet, there is no free lunch

Take what @pvanv says as gospel on tohatsu motors

 

[brodmann]

I had a 15 HP Evinrude that I went to a few boat yards and got permission to look around at all the broken down (not worth repairing) boats until I found a similar year model 9.9 and bought the cowling for it. The cowlings were exactly the same size/shape and it fit perfectly. If you get a 20 HP, you

 

[km1125]

I was surfing the ‘net and the website www.readysetboat.com has a kit that they claim converts the 9.9 Tohatsu to a 20 hp. It consists of a carburetor and a propellor. They don’t say anything about changing the ecu or restrictor plate. Is this legit?

You need to find out if YOUR motor has a carb of if it's EFI with an ECU. THEN you can look at options.

If it's EFI with ECU then Paul earlier described your options. If it's a carb motor, you do have an option to get to 15HP but likely won't get to 20.

And you have to be careful on those "carb and prop" kits. I know of one person who got a similar kit and saw absolutely NO performance increase.

 

[pvanv]

Exact model is critical to knowing how to upgrade. Year is irrelevant.

 

[Raybe]

In 3 easy steps

1. Sell 9.9 for small pile of cash
2. Empty wallet into pile to make it bigger.
3. Take bigger pile of cash and buy 20hp