I've had very good luck so far without making any modifications yet to my Avenger 85 set up. That said, I took off the jug and head and cleaned everything up before carefully reassembling it. There's almost always a bunch of milling residue in the motor even if it looks relatively clean out of the box. Other people might disagree, but you could just use the spark plug that came with the kit until you break in the motor. Mine runs like a champ with the included spark plug, and I'll switch to an NGK once I've got a few hundred miles on it. It's already such an amazing beast compared to the other motors I've owned and modified heavily. It's honestly the best motor I've owned especially for the price. That said, a CNC head is probably the next best modification I'm going to add and then an MZ65 pipe for an additional power boost.