Gunshot sound while starting

[Why Z?]

Hi,
I disconnected the blue/yellow wire as I was asking in a earlier post and left the black wire.

My main concern is upon startup, if I start with throttle closed, bike will randomly make a loud "GUNSHOT" noise when I hit the button. If I start with throttle at half-open or more, it roars to life first try.

Additionally, here is what I have noticed after disconnecting the blue/yellow wire :

Blue/yellow Disconnected :
-seems to run moderately better/less hot thru all RPMS .
-bike never backfires on decel.
-Harder starting (with throttle closed)
- (LOUD "gunshot" backfire sounds when trying to start (button)
- needs to start with throttle half open (starts 1st or 2nd time as long as I do that)

Before (With wires connected):
-seemed to run a bit hot/lean
-pipe would glow red at cruising speeds (cool outdoor temp) when throttle opened more
-started not super easily, but would start, w throttle closed. Sometimes had to kick the bike manually a couple times .