are OMC big twin 35 hp and 40 hp carbs the same?

[boatman]

Hi all,

I have a couple of 40 hp big twin carbs and have a couple of complete ’59 35 hp Johnsons. Are the carbs the same or is there any thing to be gained by swapping the 40 hp carb onto the 35 hp powerhead? You can tell it’s getting to be winter project time with questions like this popping into my head 🙂

Thanks,
Paul

[wedgie]

One difference that I can see in the parts diagram for the 59 35 hp and the ’62 40 hp is the nozzle. I believe the holes in the nozzle are bigger on the 40

[ADAM GIBB]

I believe that the throat on the 35 carb reduces as it moves toward the intake, while the 40 has the larger bore right through.

[frankr]

Also, 40hp carbs usually have an automatic choke, either water heated or air heated.

[collectorinspector]

Why ask this question?

BnC

[frankr]

quote collectorinspector:

Why ask this question?

BnC

I suspect he is toying with the idea of making 40 horses out of his 35. Not going to happen, the 40 is a bigger bore engine–more cubic inches. Back to the carburetor question, carbs are engineered to supply the correct mixture at a particular CFPM rate. Sometimes swapping works out OK, sometimes it doesn’t.

[chris-p]

Don’t swap the carbs, it will only make the 35hp run worse.

As stated above, the venturi is larger on the 40hp. It needs it, as it is more cubes. The 35hp will run like poop, you will actually lose power, not gain.

Just my 2 cents.

[boatman]

Thanks guys for the replies. Just happened to have an abundance of 40 hp carbs and wondered if there was anything to gain from swapping one onto a 35 hp powerhead.

Really appreciate all of you saving me from wasted time!

Paul

[Author]

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