Picked up a used 07 450f from previous owner, and unfortunately dont know how many miles are on it. I live in Texas where the weather is currently in the low 100's daily. Just got valves checked and the middle intake valve was on the low side and mechanic adjusted accordingly. When bike is cold (although outside temps are 100F), it fires up first or second kick with the hot start pulled in and NO choke. After riding hard for a while and bike is real hot, it suddenly stalls alot on me in the middle of holding clutch and turning slow, after that it takes approx 15-25 kicks to get started with or w/o hot start. What can be causing this? Valves just got checked about a month ago, and there is a red fuel mixture screw that may be aftermarket, but dunno if PO messed with it. THanks for the help!!