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1. Vacuum leaks around carb base. If air is leaking underneath the carb, you are going to be lean no matter what you do. Test this by spraying some carb cleaner around the vaccuum lines.
2. Point gap check minimum (prefer to go with dwell as it is substantially more accurate) Replace if necessary....bad points surface will look pitted.
3. Condition of distributor cap & rotor. If any crud on contacts...scrape it off. Replace if necessary.
4. Verify timing.
5. Verify correct spark plugs, condition and correct gap. Replace if necessary.
6. The balance between mixture screws and idle speed screw is easily thrown out of whack. If the idle mixture screws are turned in too far, not enough fuel can be provided for adequate idle speed and the idle speed screw needs to be turned out far enough to open the throttle blades to the point where fuel is provided by the main operating circuit. If the idle screws are out too far, it is hard to get decent idle quality as it will be rich no mater what you do. Screwing them in all the way, then backing out 1 1/2 turns is where to start. Small adjustments from this point.