I recently got a g660 and had trouble starting it as well honestly what has been working for me is using the decomp valve when on choke then once it turns over I put it straight to run mode kneel on the back of the saw pull the slack out of rope and then pull it with the trigger pulled. It usually starts after a few good pulls I always take the slack out of the rope before each pull it seems to start better then just yanking it over and over. Also winter here so I've only started it in 0-10 degree weather
It’s 50 to 1 not 25:1. That’s not a “fuel mixture” setting it’s a carburetor adjustment for you air fuel ratio and to set your idle. 40 :1 or 25:1 is ok for the first two tanks.
I'm having the same problem with a G660 Pro. Really not impressed with the starting compared to my Husqvarna.. though it is more powerful once running.