What Daytona said, bump the initial up to 15 & you'll see a dramatic improvement. you'll (then) need to alter the slots to get the total in line but I'd try it as for a start to get things rolling (plus richen the carb as needed). bottom line you want no pinging. Was the only change preceding the lean surge the carb swap? I wouldn't think the street demon would be lean but I dont know that carb. More info needed. Holler back