On my car, it appears that due to limited throttle opening, the transition circuit continues to deliver a good bit of fuel, even up in the 3K range (highway cruise), where the mains are starting. The combined fuel leads to a pretty rich mixture.
Dave
Dave, the transition circuit is dependent on manifold vacuum. If the throttle plates are open enough to expose some t-slot, high manifold vacuum will draw fuel/air mix into the engine. This happens ragardless of whether the mains are working or not; it's just that at higher main circuit flow this additional fuel, while still present, becomes becomes lost and insignificant in the much greater fuel being introduced by the main circuit. Conversely, if you're coasting down a hill at say, 22" hg. and crack the throttle open enough to expose some transition slot, there's a good chance you'll see the AFR meter dive rich. The mains aren't working much (if any at all) and you just introduced massive vacuum to the transition circuit.
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I have been debating on whether I should try and slow down the main activation.
Starting the main circuit sooner and limiting the transition circuit might be the hot ticket for you. I say this because the main circuit is not dependent on manifold vacuum; it's dependent on flow through the venturi.
