Mercury 20 hp conversion to 25 hp Can it be done

I have noticed that there isn

I have noticed that there isn't much difference in the Mercury 20 and 25.

I am thinking that I should be able to add 5 more hp onto the 20 that I have.

Can this be done?

How can it be done?

" I have a 115 Mercury and I h

" I have a 115 Mercury and I have posted the same question to different boat mech. I want to boost my 115 up. I would suggest that you go to the Mercury webb site, go into the motor section and compare the 20 and 25 hp motors. I think will find that they are exactly the same engine all the way to bore and stroke. The only differnce is the carb. jetting. This is the answer I keep getting about my 115 and vs. 125 hp motor.
If this is the case just take it to a trusted dealer or mechanic and have them change the carb. jets. This should get you the extra 5 hp "

"Dwayne,

The carb is the di

"Dwayne,

The carb is the difference as far as I can tell, but you should examine the two carbs before deciding that changing the jet will help. You need to measure the diameter of the carb bore. The carb on the 25 may have a slightly bigger bore.

"

Thank you for the advice.

Thank you for the advice.

I have been told that the difference has something to do with the carb in that on the 20 hp there is a "restrictor plate" between the carb and the intake. By removing this plate one should be able to find the extra 5 hp.

Thank you for the help.

" Hi,

I find it hard to bel

" Hi,

I find it hard to believe that a simple jet change will give you extra HP. If that were the case, the 115 would be running too lean and that causes a series of other problems. Many times, the bore and stroke are the same, however the porting is different and that requires a jet change to get more fuel into the motor. The early 1150 Mercury outboard differed from the 1350 by using restricted reed stops, smaller jets and restricted carb venturi. The later 1150 hp motors had different porting as well.

Your mileage may vary...

Kirk "

I had a Merc 25 HP and then g

I had a Merc 25 HP and then got a Merc 20. I was askxing the dealer what the diff was and he said the 25 is a 20 with a bigger carb and they turn it up 1000 RPMs more to get the 25 rating. The 25 did not last long and was a gas hog so he is probably right. The lower unit also has a slightly different gear ratio.

DWANYE THE ONLY DIFFERANCE B

DWANYE THE ONLY DIFFERANCE BETWEEN A 20 AND 25 IS THE CARB CHANGE THE CARB AS A COMPLETE UNIT AND YOU WILL HAVE A 25HP DONE IT MANY TIMES. JUST SO YOU KNOW I AM A MERC TECH AT A LARGE O/B DEALER GOOD DAY