I am reading my service manual for my 09 yz450f and I have noticed that my bike runs quite good ( the tiniest bit of decel pop, very strong mid range and top end) except when I open the throttle quickly. It boggs badly and sometimes puffs out flame. Anyways My manual is telling me that this is caused by the leak jet not being correct. I am running it stock #55 with it adjusted to the manuals specs. My point is the manual must have been translated from another language and I do not understand it. It says -If the engine breathes hard in quick throttle openings select a leak jet having a lower calibrating number, then it says -If rough engine operation is felt in quick throttle openings select a leak jet having a higher calibrating number. Can any one tell me what the hell the difference is between these two definitions, my bike just boggs down I dont know if that means breaths hard or if that means rough engine operation. Does anyone know what the hell Yamaha means?