My YS 110 starts first time for its first run of the day, after I spin the prop over with the starter, with the throttle open for 8 - 10 seconds.
However, it dosen't want to start that easy for its 2nd, 3rd run etc.
I'm not sure how much priming it needs.

It's mounted inverted, uses 20/20 fuel and I release the pressure in the tank straight after each flight.

I can't remember what I used to do when it was mounted on its side in a previous model, but it used to start easily every time then.