[vector1]

i suggested changing the msd chip earlier, but if it is only happening in first i doubt this is the culprit. does sound like a fueling problem, uncovering something or running out of fuel in the carb or going rich. o2 sensor in the exhaust would tell a lot. i would try it without the air cleaner, and make sure the exhaust is not restricting, simple stuff to start with. you might go through a lot of tires before you find this.