with a big cam there isn't enough vac to hold down the metering rods during idle. They stay up at full rich. The air/fuel screws do little if anything in this condition. I've only seen this problem with eddies when installed on big cam motors. Mine only had 7 inches of vac at idle in park and 3 to 4 inches at idle in gear. Now with initial timing set at 20 car runs super with no stumble. But did need to recurve the mech advance in distributor to keep total at 38 degrees