Blow-back during warm engine start

[Yvan]

I use MJLJ for my BMW 1.6 LPG fuel only engine. I created ignition map, and it runs OK apart from one problem.

When the engine is warmed-up, I get single blow-back when starting (the very moment it starts) if I slightly press on a throttle pedal.

This does not happen with my original ignition system. I am about to record ignition map of BMW original ignition system (I just managed to repair my timing light) when weather allows.

I attached my ignition map. Why is this happening? I guess too much advance, or too lean mixture. If you look at the map you should know that LPG wants more advance at low rpm, and less at high.