This will cause a phenomena called “puddling” where little droplets ofgasoline adhere to the intake manifold runners. Setting the idle for the highest vacuum idle reading will result intoo little clearance of the throttle plate forcing too much of the idlemixture through the lower idle port and too little through the idle transferslot. Exceptions to thisare GM carburetors with the idle speed air screw, and end carburetors ontripower. This clearanceallows for maximum velocity of idle air past the idle ports. Most moderncarburetors are designed to function with roughly 0.020 (20 thousanths)clearance between the center of the throttle plate edge, and the throttle bodyat a point equidistant from the throttle shaft bearing areas.
Bog from a stop isvirtually always (and generally erroneously) diagnosed as a faulty acceleratorpump (see the section on “accelerator pumps” for testing). We will discuss twotypes of bog: the first is bog when the vehicle is accelerated from a stop thesecond is bog when the vehicle is accelerated from cruise. This paragraph also applies torelatively stock engines with the original carburetor. Constanthesitation is covered under “surging”. This paragraph applies toan instantaneous bog, hesitation, or stumble upon acceleration.
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