Hey everyone I have a 2002 Yamaha raptor 660r that has the big bore kit and some other work done to it. It idles all day fine but when I try and take off in first it starts to die. I give it like 60% throttle and it will do fine but the whole time it’s in first it back fires and cuts out. As soon as I shift to 2nd it clears right up runs fine. I know all the vac lines to the carbs are good. Any suggestions?