Converting 25hp 3 cyl to 35hp

[WhiteRice]

I've searched a little and read through a pot back from 2004 where a 20hp was converted to a 30hp by simply switching the carbs out. I don't believe this was a 3cyl as mine is. ( 1996 E25RMEUR). My motor sits on a 16ft C.S and with three ppl plus fishing gear, I can plane out at 22mph. Flying solo I can hit 26mph. I'd like to get into the 30s and due to the build of my boat (center console is mounted much further to the back) I feel adding a larger motor (extra weight) may do more harm than good. Has anyone converted a 3cyl 25 to a 35? I've looked at the schematics here and most of the parts are shared between the motors as it relates to the fuel system. The reed valve assembly appears to have a diff part number but the intake manifold is the same. Apart from switching the carbs and possibly changing the reed valves, what additional work would be needed? Timing adjustments? fuel pump upgrade, etc? Thanks in advance...

 

[racerone]

You would want to install the bigger diameter pistons would you not ??

 

[WhiteRice]

Did I miss something when looking? The piston part numbers between the 25 (mine) and 35 (E35KLEUR) appear to be the same...

 

[Rustywrench]

The 25hp 3cylinder motor is a 500cc motor while the 35hp is 565cc. Look closer at the parts break down. Shows both pistons together, but specifies 25hp or 35hp as different part numbers. Both standard bores & oversizes.

 

[WhiteRice]

Thanks Rustywrench. Didn't expand the part link for the piton on the website...

 

[racerone]

You agree then that the 35 uses bigger pistons !

 

[WhiteRice]

Let me clarify my questions as well... Would adding the 35hp carbs (plus any other necessary components) be worth the time, effort and money to get into the 30mph range? I've looked at a few used Yamaha 40 2 strokes that are only about 40lbs heavier but with controls will run about $2800. Just wanted to see if there was any experience with this carb upgrade on these smaller 3cyl

 

[jimmbo]

In a word, no. The 35 carbs will probably be too big, resulting in lower velocity in the Venturi resulting poorer overall operation. Unlike the 2 cylinder 25 - 35 line, your engine has three carbs, so it can get expensive. Also, then there is the issue of how to get the proper sync between carb and spark.

to get those extra 4 or 5 mph will require about another 20 hp

 

[WhiteRice]

Thanks Jimmbo. 30mph would be nice but not a necessity at the expense this could incur. I should just be happy it runs well now