Bike Dies

[Why Z?]

Just got the bike. Had 5 miles on a brand new complete rebuild when first bought it.
My confidence and trust in the person who did the work is pretty high. He is (and verified to be) a mech for a major power sports company and former gasgas rider/racer.


Not long after getting the bike home, at about 30 miles I started to experience some hard starting and the bike has died a few times on decel, normally after being at cruising speed and then shifting down (and having clutch pulled in) a couple times the engine has just cut out completely.
Then usually has started back up, sometimes with 2-3 pushes of the button.

Details:
Hard starting -
-usually when started for the 1st time of that day. (Doesn't have difficulty when it is started after being shut off for only a few hrs).
-temps : Normal 50-65 degree weather cond.
- usually emits a "POP" on one of the failed starts.
- seems to help if I kick over a couple times (which have never successfully kick started the bike )
- kicking: never successfully kicked this bike to life. (Yes I am lil 120 lbs but have had no issue kicking a wr450f and yz250fs, this one doesn't wanna kick --- my dad who is almost 200 lbs couldn't kick it either)


Any ideas/suggestions ?

Edit: I LOVe LOVE LOVe this bike. If there is a problem I can correct I want to do it right away, because this is THE BIKe of my dreams... But I don't want to lose confidence....