I've been using the old FP on my 2000 Honda VFR (800cc/V4) engine. Previously using the old Amsoil PI as a maintenance dose, a look down the throttle bodies showed shining clean intake valve necks in the head. This spring, the inspection showed some really dirty, deposited intake valve stems. I used some Power Foam and Amsoil new PI in two tanks of gas, and now they are clean again. Thus, after a season on FP, the valves were not kept clean like on the PI. I'm wondering if my switch to FP from PI in my cars also had the same negative effects. Betcha it did!! I'm not convinced anymore that the FP is a good intake (valve) cleaner compared to the other "labelled" fuel system cleaners.