Float level on DCNF/13

Refer to birdmans 308 guide where he has given a detailed description of how to adjust the floats and tune the carbs. I have personally adjusted the floats and tuned my 308gtb, you will really love the sound of a perfectly tuned engine. As for your query I think it is from the highest point.

 

The float height is measured to the body of the float and not the seam.

I was taught this by an old time Weber carburetor expert who has every Weber special tool. Most of which you cannot buy anymore. The float height gauge that he is was a thing of beauty, made of solid thick brass with settings for every float height that Weber/Ferrari ever used. It made setting float heights easy. I have never seen another one.

 

I would not trust any manuals that were not published directly from Weber itself.
There is a slight difference between the two measurements, but it is not too great.

There are a few things to take into consideration when jetting carburetors:

You also have to remember that the composition of the gasoline has changed greatly since the original carb jetting specifications were created. Modern gasolines have much more oxygenators/alcohol in them then back in the day when your car was made, and have the effect of leaning out the fuel mixture.

Not all engines and carburetors are created equal. Differences in engine tune :compression and cam timing will have an effect on the needed fuel mixture. Carburetors have different jetting for different markets for emissions purposes (USA Smog laws).

Individual carburetors can have casting differences. Generally vintage Webers were of very high quality, but some modern reproductions are terrible (to the point where they barely function). The old time Weber guy in our shop had a bench set up so that he could pressurize the carb with fuel at the correct fuel pressure, then remove the carb top and check the fuel level in the emulsion tube fuel well and see how high it was as compared with the port in the side of the well for the fuel delivery. He would then set the fuel level in the carb so it was a specified distance below the port (2 or 3 mm). This is the only way to do it for special racing carb where there are no float height specs, or for poorly manufactured repro. carbs.

The stock carb specifications are a good starting point, but sometimes you must make changes for best performance during dyno testing or just seat of the pants driving.

The other thing is that Ferrari took the DCNF carbs and intake manifold from the Fiat Dino, with its engine mounted longitudinally and turned it sideways and stuck it in the 206/246 with out any regard about the fact that the carbs were not designed to work this way. Under hard cornering the fuel levels in the carbs change drastically, causing a major hesitation/fuel starvation issue after rounding a hairpin turn. Ferrari was smart enough to correct this on the 308 GTB/Dino series of cars.

That said, I would set all the carbs with the same method, and then test drive it and make any adjustments as needed.