symtoms of lean and rich mixture

I've found sniffing the exhaust only good for idle mixtures, which can be a problem with other-than-stock camshafts. Use the spark plugs. Set the timing first, then set the carb with a vaccum gage for the highest reading at the specified rpm..I like to stay under 850rpm, 650-700 for a stock engine. Once that's done..replace the plugs. Then, take the car for a ride. Bring a sprak plug socket, and stop after a few miles of mixed throttle driving. Pull a plug..Watchout, very hot, so use an extension and/or mechanic's gloves.. As they said, it should be tan..the lighter the beter, IMO, but it should have some color. very lean can cause surging, intermittent misses, studders, and running hot, in addition to issues with bearings, pistons, and rings. Too rich is loss of efficiency and power, ignition issues, in more extreme cases ring damage , and visual clouds of smoke and black deposits on the rear end of the car..(Seen a TON of car show vehicles with that...)