It could be either an ignition problem or a fuel problem. (yea, I know, real good answer! LOL)
It could be a plug misfiring from being a tad lean, or worn, or partially fouled, or a wire breaking down too.
It could also be an occasional drip of fuel from one of the primary carb nozzles, momentarily fattening up the mixture. You can look down the carb with a flashlight and watch for the drip.
The ignition problem may take a little more checking.