Stihl fs91 starting

[Connor 095]

My Stihl fs91 starts first time every time but to do that I have to hold the trigger down while pulling the starter rope as opposed to just priming and setting the choke. What could be causing this ? 

[woodwoozles]

Blocked filter? Air or fuel?

Poor spark, fueling possibly gone out of adjustment bit unlikely, or crappy fuel.

Breather pipe trapped squashed or broken pipe/fuel hose?

Just ideas as without fault finding and without it infront of me difficult to tell.