I plan to check the air/fuel mixture on my carburetor (Holley list #3247) this weekend using a vacuum gauge and have a couple of questions: 1) I plan to hook-up the vacuum gauge to the fitting on top rear of the intake maniold. Should I plug the vacuum advance line?; 2) the 1966 service manual mentions that each mixture screw should be turned in until seated then backed out one full turn (others say it should be backed out 1.5 turns) and then adjust for highest possible vacuum. Is there a need for me to turn each screw in to seat and then back out? Could I notjust hook-up the vacuum gauge, check the reading and then adjust each mixture screw from its current position in the carburetor? Thanks for the feedback!
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Re: Carburetor Fuel Mixture Adjustment
John:
Do not plug the vacuum advance line. Leave the vac advance connected, get the engine to operating temp, idling in neutral(or park). You will need manifold vacuum, not ported vacuum, so tee into the vac advance line with your vacuum gauge. I do not know which vacuum tap you refer to in the back of the intake manifold, but if it exists, it will certainly be manifold vacuum-use it.
Recommend turning the screws GENTLY into closed position to ensure a balanced adjustment on both venturis. Be sure to count the turns on both needles when turning them in, then back them both out one turn as recommended as a starting point. I use a tach and dwell meter and/or my ears in addition to the vac gauge, and adjust for the highest and smoothest idle.
BTW: The needles on my Holley 2818 yielded the best idle @ 3/4 turn each.
Joe
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