I have been having a similar problem, But mine will start occasionally. I put a 450 kit and the short air. Motor ran before but in a different bike. Sometimes it will start right up others while missing with the throttle. Same thing even when warm.
from the boot to the runner,i used a nut driver to tighten mine down not a screw driver.I had a small leak and it compounded my problem once i made sure it was toght then i found the big problem