Hey all. Does anyone know what cylinders are being fed by the driver side idle mix screw.

Do these screws being too lean or rich affect acceleration as well or just the idle? Should they be turned EXACTLY the same amount?

I am trying to chase down a engine shudder at 1200-1400 rpm.

I have a 312 with Fordomatic.





Thanks

Drivers side controls 1-6-7-4

Pass side 2-5-3-8

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

Idle mixture screws affect idle air fuel mixture and low speed air fuel mixture up to a certain engine rpm (unknown to me) . Subsequently, there is a transition to the 'high speed' metering system within the carburetor.



The 'idle' mixture screws are backed out from where they 'seat' an equal amount for initial engine start-up when a carburetor is initially installed.



Carburetor adjustment is done AFTER plugs have been gapped, distributor to carburetor vacuum advance hose or line disconnected at distributor and plugged, idle speed r.p.m adjusted, points (dwell angle) adjusted, idle speed rechecked, dwell angle rechecked, ignition initial timing set, and subsequently, engine idle speed again checked to be correct. Engine should be at normal operating temperature for carburetor adjustment.



Use an intake manifold connection for hooking up a vacuum gauge. Adjust one idle mixture screw in-or-out to obtain maximum engine vacuum. Adjust this screw in small increments leaving time after each adjustment for the change to stabilize.



After doing the one idle adjusting screw, do the same with the second adjusting screw.



IMPORTANT: After doing the second adjusting screw, go back and go through the process again, first with the first screw and then the second. I usually find myself doing this a third time as well. ALSO: As you make the individual idle screw mixture adjustments, recheck and adjust engine idle speed r.p.m. on each as you 'finish' making that individual screw's adjustment. -The mixture screw adjustment can significantly affect engine operating r.p.m.



ALTERNATE PROCEDURE:

Instead of using a vacuum gauge for measuring engine idle screw adjustment 'performance', use a tachometer. Procedure is basically the same, except instead of looking for the highest vacuum reading, look for the highest engine operating r.p.m.



AS BEFORE: After doing the second adjusting screw, go back and go through the process again, first with the first screw and then the second. Again, I usually find myself doing this a third time as well. ALSO: As you make the individual idle screw mixture adjustments, recheck and adjust engine idle speed r.p.m. as you 'finish' making that individual screw's adjustment.



IN FINISHING UP, reconnect the distributor vacuum advance line or hose from the carburetor. If this is an automatic transmission vehicle, apply the parking brake, block the wheels, place the vehicle in 'Drive', and readjust the engine idle speed.



Hope this helps!


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York