Fuel economizer setup for Johnson 35HPs adapted to 25HP?

[mr-asa]

Evening gents.
At the latest Florida meet a few of the members were talking about how the mid-late 50s 35HP Johnsons had a fuel economy carb/ignition setup, and you could adapt that setup to the 25HP motors.

Does anyone know what I’m talking about? If so, can you provide pictures, parts lists, etc etc? I’d love to pick up the parts and get it setup on my 25HP

I was told you had to get the 35HP carb, and everything that bolts underneath the mag plate of the 35HP

[vintin]

I’ve heard more than one person say the 25hp ran better than the 35hp and I’ve seen them in action.

I’d be careful what you do.

[chris-p]

Interesting thought. Have never tried it myself.

I would have to think though, that the added fuel from the larger vacturi would negate any savings you would get from the setup!

I would stick with the original 25hp setup, and back off the throttle a touch once on plane. Just my 2 cents.

[frankr]

Hm.m.m., yes I know what you are talking about. What I do not know is how it will run with the bigger carburetor. Maybe OK, maybe not—I just don’t know. Might be safer to use a 1956 30hp carburetor. At least that would be the same engine displacement.

Let me know if you want me to post a marked-up parts list.

[mr-asa]

One of the people talking about it was Steve Wood who said he had tested it. His standards are probably higher than mine, so I figured it was a sound idea. I might have one or two of the details off, though so it may need correcting as it’s fleshed out.

Frank, I’d definitely like a parts list

[frankr]

The theory behind the fuel saver is that you bring the boat up on plane at full throttle, then back off on the throttle to the "cruise" position. That keeps the spark at full advance but partially closes the carburetor butterfly, presumably saving some gas. It works somewhat on a boat with adequate power. But if the motor struggles to maintain speed at WOT, then backing off to cruise throttle will lose the plane.

[frankr]

Give me a bit of time to mark up and post the parts list.

[mr-asa]

quote FrankR:

The theory behind the fuel saver is that you bring the boat up on plane at full throttle, then back off on the throttle to the "cruise" position. That keeps the spark at full advance but partially closes the carburetor butterfly, presumably saving some gas. It works somewhat on a boat with adequate power. But if the motor struggles to maintain speed at WOT, then backing off to cruise throttle will lose the plane.

Interesting, considering I’m planning on running my 25HP on my Herter’s and everyone looks at me like I’m mildly crazy for doing so, hopefully there won’t be an issue with losing plane. Of course, I haven’t even got it water worthy yet.

I’m in no hurry.

[frankr]

Best I can do from memory. May be a gotcha or two in here. This is a 1957 35hp

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[beerman57]

So what’s your Herter’s? Big and heavy / small and light / in between?

[Author]

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