If I were to pickup the HMF slipon DO I HAVE TO REJET? Some people say yes some say no?!?!?!?! Well I know I should put the jet kit in for best performance but what if I wanted to just get the slipon for now. I know the jet kit helps on the air/fuel mixture into the engine but on the exhaust stroke the intake valves are closed and the exhaust is pumped out so if you say yes I have to rejet by adding a slipon can you explain why? By adding a better flowing exhaust why would it call to rejet? The intake and exhaust strokes are 2 different actions?! right....

any input would be appreciated
thanks

 

The HMF pipe has less back pressure so the engine is breathing better taking in more air. More air leans out the air fuel ratio, so if you do not want risk burning a piston you will need to put larger jets in the carb to give the bike more fuel to compensate for the air increase, and by burning more fuel and air you get more horsepower.