Put a 7" by 3" G/F 3 Series Master Airscrew prop on my NV .074 engine. Still running Byron Genera 2 fuel. (Has 15% nitromethane and 20% oil.) The motor peaks at 15,660 r.p.m. The lowest I can get a steady idle is at 3,880. Any lower than that and the motor will die. That small screw which has an offset head is needed. I took it out thinking I would get more peak r.p.m. WRONG ! All that happens is the intake inlet bar goes off center and the motor would LOSE r.p.m. ! This is one STRONG engine ! Am very impressed !