husqvarna chainsaw 142, wont tickover?

142 has been a poor starter, I changed petrol and oil 2 tmix, and set spark plug gap to 20 thou.
Got it to start but had to keep blipping throttle to keep it running.
Being smart I thought I could solve this by leaving choke half open - few minutes later I had melted chain brake.
Then removed chain and bar & restarted 142, still wont tickover, tried screwing in the throttle stop, this helps, but will be no good when bar and chain on, cos chain will be engaged all the time.

Can you help, what about l and h screws?