A 6lb pulley in the Harley over stock is okay. The stock tune is pretty damn good up to that point, anything after that... no dice. I've tuned plenty of them (HD's) at 6lbs over stock and while there is extra power to be picked up with tuning in stock form the A/F ratios are pretty good, and sold a ton of 6lb pulleys to Harley guys who left the tuning stock. You're only getting about 4lbs actual boost over stock with it because of the upper pulley, and even the Lightning can be run without an aftermarket tune at with 4lbs over.