The 2->1 adapters work about like merging two lanes of heavy traffic into one lane.
At low speeds (RPM), not a problem.
The higher the speed (RPM), the worse it performs.
Zenith made single barrel carbs in the size 3 throttle with both larger venturii, and smaller venturii than the varijet, depending on your desires.
All of the Zeniths are (opinion) more reliable than the varijet. Some come with an externally adjustable main metering jet. Some come with an adjustable throttle arm.
The bad news: they don't cost the same as a varijet (wonder why
).
Jon
