The mag, can you hear the impulse function clacking while cranking? If it's not, there won't be enough spark at cranking speed. Have you checked the ignition timing?
What kind of wires did you use? Mags need wire core wires, not resistor, especially not carbon wires.
Since the rebuild, have the valves been set? Always a good idea to retorque the head bolts and set the valves after the first run up to temperature.
Is the air cleaner properly serviced and free flowing? They can be internally clogged with dirt or mouse/bird/mud dobber nests. So can the exhaust.
The carb should be adjusted last after everything else has been checked out. The carb needs to be properly functioning, not flooding, be supplied with plenty of fresh, clean fuel, no vacuum leaks, choke and governor linkage properly adjusted and working.
Once running, look and listen! Balky and weak usually means too lean. Blubbering black smoke is too rich. With the engine up to operating temperature, idle set as slow as practical, adjust the idle mixture for best idle. To adjust the high speed, idle the engine down, turn the high speed adjust in 1/4 turn at a time, open the throttle suddenly. Listen for the response. Keep leaning the mixture, repeating the test until it lean balks on quick acceleration. Then start backing the mixture screw out 1/4 turn at a time until the engine will take sudden full throttle from idle without hesitation. A touch of black smoke is good, it should clear up as soon as the engine comes up to speed.
As for the plugs, once everything is properly adjusted and some up to temperature running, preferably under load, the plugs can be 'read'. Look at the inner insulator, if it is brown, the plugs are in range. if black, they are too cold, white is too hot.
Again, everything works together. If any one thing is neglected or out of tolerance, results will vary! If the engine has been run rich, the oil may be contaminated with gas. That will change the carb adjustments and plug color. Change the oil if in doubt.
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