hi, new to forum, working on 400 foreman, runs ok w/ choke on. idles fine w/wo choke. no power w/ choke off, lots of exhast backfire, some in carb. poor gas?, coil voltage low?, has some blowby: oil in filter, acts like it is leaning out on accel...choke on 1/2 runs ok. been in carb, jets are clean, blew all passages out. would poor compression cause this, used bike, has run this way since purchased. no mods on it, question rejetting richer????