The diaphragm fuel pump on 4 cylinder Lycomings and perhaps others, generates output pressure referenced to crankcase pressure. My carbureted engine has a 7 psi pump, so if I pull case pressure 7 psi below induction pressure the float bowl will soon be empty. Likewise, if I restrict the vent and pressurize the case, fuel pressure will go up, maybe enough to force fuel past the needle and flood the engine. This might be a good place for the “Keep It Simple” and reliable rule.
BILL HANNAHAN
WFHANNAHAN@YAHOO.COM __________________________________________________
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