Ok, I will answer, but it isn’t free, you have to think on it and answer it yourself, I’ll just set it up.
Look at it a different way.... why not?
Putting float level high on primary does what?
Makes fuel easier to pull from booster since it doesn’t need to lift as far.
What is the negative? Well hard acceleration and fuel will spill from booster.... but under hard acceleration the boosters are online anyway, so no biggie. Might argue that it’s beneficial.
Ok, now secondaries, why are they low?
Low fuel level makes it less likely to spill? When would it spill? Hard braking.... the EXACT time you do not want excess fuel in the intake.
Alright, so that is technically the answer.... now for the work around!
Ok, so fuel is harder to pull from secondaries due to lower float level. Greater pressure differential is required to pull fuel. How is this dealt with?
Ok so lets look at basic calibration of a common carb an 1850.
In the primaries we have:
So we have a large idle air bleed at .067
Idle feed restriction for fuel is .026
We have a high speed air bleed at .031
So looking at high speed, what does .031 feed? It puts emulsion air into air well. This bleed air enters high into the emulsion tube via. .026 passage. Tube has 4, .025 holes right at float level.
Std emulsion from air well to main well is 2@.028
What does this do and why?
Why does putting air in right at float level matter? What dies it accomplish?
Moving onto, the secondaries:
Idle air bleed is .028
Idle feed restriction is .031
Ok.... how is this idle circuit different than the primary? Why?
Secondary High speed bleed is .025
How does a .031 hsab act differently than a .025?
Explain in detail and it all becomes clear.
Another work around, angle channel primary vs secondary metering block, different angle for same reason.
Now lets toss the wrench into the gears... you check float level via this plug right?
A minor angle is present in how level the carb is fore and aft.
Now mount two carbs backwards 😆
Please remember each carb was designed for a specific engine. Float requirements are different for different carbs. Thus some float bowls have different sight hole locations. All part of the overall system.