The idle jet is set when the engine is running at it's slowest RPM. That means the throttle plate is closed and the engine is indeed running off the idle circuit. Once set, back it out 1/8th to 1/4 turn for optimum performance.
As for the fast idle jet, spin your engine up and use a timing light to set the maximum spark advance. Once the timing is set, adjust the fast idle jet until the engine runs the best. Make sure you are still idling well and readjust the speed idle as needed. The high speed jet SHOULD NOT affect the slow speed idle jet but on initial settings it may. What makes the engine run best is making sure the timing is dead on 180* out from the top cylinder. Easily done with an ohm meter if you need to do that. It's when the points open that you set the timing to TDC...
