Carburetor Theory: Idle Mixture

This I simply don't understand. I put a rebuilt Motorcraft 2150 2v carb on my 1977 F-150 400m Engine, and then set about adjusting it per the tech manual. I had only one problem: when in "park" the idle was fine, but when I put it in "drive" the engine died. Ok, fine, call for help. I contacted the local carb expert and he said one phrase: "weak idle". The mixture was too lean. So I adjusted the mixture properly this time (yeah I screwed up), and it worked great!

Now the question: why?

Why does a load on an engine with a lean mixture cause the engine to die?

Thanks,

Cy

Reply to
cfoughty
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Because the lean mixture (or, for that matter, an overly-rich mixture, or any of numerous other "state of tune" isses) does not permit the engine to develop enough power to take up the load, only enough to keep running with no load applied.

Reply to
Daniel J. Stern

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