Johnson/Evinrude Carburetor Conversions

[oring1]

How much of an increase can you make on a 15hp two cycle motor by upgrading the carburetor? Can you go from a 15hp to a 40hp? I would like to understand what specs must be compared and how/where to get those specs before trying to make a conversion.

 

[Chinewalker]

None. The 15 hp OMCs are already maxed out. Within some families of motors, .ie motors that share the majority of parts, stroke, bore, etc. there is usually one that is maxed, with one ore two other detuned versions that use smaller carbs, but adding a larger carb to the top model won't do anything but make it run like crap. Too much fuel is just as bad as too little.

 

[F_R]

None. The 15 hp OMCs are already maxed out. Within some families of motors, .ie motors that share the majority of parts, stroke, bore, etc. there is usually one that is maxed, with one ore two other detuned versions that use smaller carbs, but adding a larger carb to the top model won't do anything but make it run like crap. Too much fuel is just as bad as too little.

Agreed, what Chinewalker said. If a big carburetor were the secret, you could slap a 40hp carb on a 3hp, and blow everybody off the lake. Actually, the problem with a too-large carb is slow air velocity. The air flowing through the venturi is what makes it work. A certain amount of air flowing through a small hole flows at a greater velocity than the same amount of air flowing through large hole. The amount of air flowing is mostly due to the cubic inch displacement of the engine---and of course the RPM. It's all related and that's why engineers are paid big bucks to design it.

 

[oring1]

Thanks for the feedback! You have saved me a bunch of time and money.

 

[oring1]

Can you upgrade en Evinrude 9.5hp? Can it be upgraded to 25HP or greater?

 

[F_R]

Dream on---

 

[tomhath]

How much of an increase can you make on a 15hp two cycle motor by upgrading the carburetor? Can you go from a 15hp to a 40hp? I would like to understand what specs must be compared and how/where to get those specs before trying to make a conversion.

Horse power is a function of two things: torque and RPMs.

Torque is primarily determined by displacement (other factors like compression play a smaller role), feeding it more fuel will not increase the torque.

You can try to get more RPMs by running more fuel through it up to a point, but the motor is designed for a maximum speed and exceeding that you risk turning it into a grenade. You would need to spin it somewhere around 15,000 RPM to get 40hp out of that engine - in other words, not going to happen.

 

[jimmbo]

Can you upgrade en Evinrude 9.5hp? Can it be upgraded to 25HP or greater?

You have to be pulling our legs.

 

[flyingscott]

Yes you can upgrade a 9.5 to 25 hp it is easier than most people think. This is the procedure
#1 Put ad to sell 9.5 on craigs list.
#2 wait for sucker with cash.
#3 sell to sucker with cash
#4 Put money from 9.5 in your wallet.
#6 Look on craigslist for 25 hp motor.
#7 find 25 hp you like.
#8 take cash from 9.5 plus extra out of your wallet.
#9 give cash to seller.
#10 take 25 hp motor home.

There you go 10 easy steps to turn a 9.5 into a 25 hp motor for mostly free.

 

[jimmbo]

Yes you can upgrade a 9.5 to 25 hp it is easier than most people think. This is the procedure
#1 Put ad to sell 9.5 on craigs list.
#2 wait for sucker with cash.
#3 sell to sucker with cash
#4 Put money from 9.5 in your wallet.
#6 Look on craigslist for 25 hp motor.
#7 find 25 hp you like.
#8 take cash from 9.5 plus extra out of your wallet.
#9 give cash to seller.
#10 take 25 hp motor home.

There you go 10 easy steps to turn a 9.5 into a 25 hp motor for mostly free.

I will concede that is an 'Upgrade'