I bought a bike from California and it's having (what I assume) air/fuel issues. I have to turn the choke all the way up to get it to start and then it jumps to 5k rpms and I drop it down. If I attempt to take off, it usually stalls. The throttle isn't too responsive either, unless the choke is all the way up (and it's not all that responsive then either). I'm new to motorcycles, so bear with me. It's a 2004 Kawasaki Ninja 250. The guy I bought it from said the carb jets may have to be changed due to the altitude. Any ideas?