johnson 1980 25hp seahorse carb

[Happybro]

Hello. I'm planning on getting a Johnson 25hp 1980 and I have seen people doing stuff like replacing the carb with a 35hp carb to go faster (and change the timing) so i was wondering if i could just drill out the carb on the 25hp carb and change the timing. Would that work? because I red about someone saying you don't need to change the air intake so i though you could drill it out. Any ideas?

 

[Tim Frank]

Short answer is "No".
If the 25 HP is a good runner, don't mess with it.
If you really want a 35 HP, start with one.

 

[oldboat1]

Get a 35 carb if you want to play around (rebuild it or just disassemble and thoroughly clean). Might satisfy curiosity.

think you will go back to the stock 25 carb, but lot's of readers here share your curiousity (I'm an old stick-in-the-mud, but the topic comes up a lot in one version or another. It's all fun.)

 

[Happybro]

Get a 35 carb if you want to play around (rebuild it or just disassemble and thoroughly clean). Might satisfy curiosity.

think you will go back to the stock 25 carb, but lot's of readers here share your curiosity (I'm an old stick-in-the-mud, but the topic comes up a lot in one version or another. It's all fun.)

so you are saying that its just as fast with the 25 as the 35? I just would like to do tubing with this on a 12ft aluminum v hull boat. so i though maybe that would be doable. if not would drilling it for 30hp work? I just saw that this guy did the 35hp carb (https://www.youtube.com/watch?v=pg7N7Mu3CsU) any ideas?

 

[oldboat1]

Yes re. carb switching (all in all, 25 as fast, maybe faster -- imo. Low end almost surely smoother.) May want a bigger boat, bigger motor (14-16').

 

[jakedaawg]

It'll be easier to just figure out how to mount the motor on the tube directly

 

[Cat nip]

The bore size is bigger not just the jets. So simply drilling them out is not an option. The blocks are the same but in some the porting in the cylinders was slightly different from the lower hp ones to the higher hp ones.

 

[jimmbo]

Intake had a different plenum, reeds and stops and there were differences in the inner exhsust cover, which affected exhaust tuning.
Putting a 35/30 carb on the 25 will make for erratic low speed operation, flat spots on rapid throttle opening.

 

[flyingscott]

You will.have a bigger problem if you make the conversion. A 25 uses a different lowerunit than the 35 hp. The 25 lower unit is not a robust unit. The 35 hp lower unit was not a great unit either either.