[vettestr]

Doc,
Checking color of spark can be done by pulling any spark plug wire off its plug. Insert an old plug in the wire you removed and place the plug threads against any metal (header tube or any engine part) where you can see it easily. If you do not have an old plug it will jump out off the boot end anyway. Now start the engine to see what color jumps out the wire or across the old spark plug. Let it run just long enough to see color of the spark. PS... avoid a polished valve cover as spark may discolor a small amount and do not hold the wire or move it while running or you may get zapped. LOL.

A cold engine will run with a very rich mixture (think about a choke) but a warm engine wants a better air/fuel ratio. Closing just 1 side should kill the engine and should not have to seat both mixture screws to kill engine. Try the loaner carb to save a bunch of time and grief for yourself. Jeff C