I am fixing up a 2000 yz426 for a buddy and am having some problems. I put a new air filter on, changed the oil and then got to the carb (yuck). It sat for a couple years and needless to say was gross. I pulled it all apart and cleaned everything. When I put it all back together it fired right up on the choke but runs horrible off the choke. I turned in the idle screw and it seems to run a little better but when i let off the throttle it pops really bad. I am new to 4 strokes but have worked on 2 strokes for years. Any ideas would be appreciated.