ok, when you make a change, like adding a pulley, of course you change how the factory intended the engine to perform.with the supercharger Pulley, you spend the supercharger faster condensing more air into the engine. Now you need to add fuel to balance everything out. AFR= air fuel ratio as I said before, the factory sets the air fuel ratio between 9.9 and 10.7 . That's where the black smoke comes from. Sometimes when you take off, and of course your exhaust tips are black with sutt.. By retuning the computer,to either add or take away timing and fuel and a few other things that I don't know about, they can set your AFR's in the correct range. The pulley that you ordered most likely will not increase the speed an off cause any problems. Originally I had bought a code three pulley,,62mm, installed it on my car without a tune or intake, the AFR is fine.they were reading like 11.1,, with a retune I brought My AFR's up to 11.9..

Let's say that your AFR stock are running 10.2, which is about right, you had the pulley with it being a 64 mm you probably only add 5 to 6 points with your pulley, so your AFR should be somewhere around 10 9 to 11.2
I would shoot an e-mail off to wherever you got the pulley, and tell them you do not have an AFR gauge, and you would like to know if having this pulley is going to take your AFR too high. You have to remember, the only time that this is critical is that wide open throttle ( wot) so if you want a family on and just jump on it ever so ever so often, do it and enjoy it jim

GOGGLE Air Fuel Ratio