spark at the plugs

[Bill OH]

Maybe one of the idle circuits in the carb is fouled with debri. Try removing the idle adjustment screws, give the holes a good shot of carb cleaner followed by compressed air and do this a couple of times, put the idle screws back in and adjust - see if that solves the problem. My thinking is that an idle circuit of the two is fouled for the motor runs okay on the main circuits.