25 Evinrude switch to 30 hp ?

[Sylva-Ranger]

I have a 1985 20 hp Evinrude CE20CRCOS on a Naden 16' aluminium boat.

I laso have an old 1989 Johnson 30 hp for parts (missing lower unit and have a bad power head)

​I think i can upgrade my 20 hp just changingthe carburetor/intake from my 30 hp ?

​if is the case, do you think il possible to have a less smooth idle for trolling that ik i keep my 20 hp original ?

​Do you think i have a real gain or i'm better to stay to 20 hp ?

​I dont really nedd more power, but thinking the possibility to have 10 free more hp

​Thank you.

 

[F_R]

You would have to sit down with the two parts books to find the difference. Better you than me. But my guess would be maybe 2 mph difference--not enough to tell by the seat of the pants feel.

 

[jasper60103]

Johny25 did a very good job documenting his conversion and results. Worth a good read...

http://www.tinboats.net/forum/viewto...0c374e96048cfd

 

[ondarvr]

To your question about the idle quality.

​When going to a larger carb there is frequently some sacrifice in low speed performance, but not always. You gain on top, lose some down low, it's all a compromise.

 

[Sylva-Ranger]

To your question about the idle quality.

​When going to a larger carb there is frequently some sacrifice in low speed performance, but not always. You gain on top, lose some down low, it's all a compromise.

Thats
​the reason why i ask this question.......And if it for gain just 2 mph like F_R said, i probably dont do Nothing.....

But before i whill read the link that give Jasper.from A to Z

 

[jimmbo]

Other differences could be the intake manifold and reeds, and differences in the exhaust cover/tuner. As F_R said you have to go through both parts lists(at a dealer, online lists are notorious for typos) looking at all the parts in the powerhead, induction and exhaust for differences. On some engines there were changes to the throttle cam(affects carb and spark sync) between HP ratings