Read the docs from Stihl and you will see that they tell not to store the saw with gas in the carbeurator. The recommended procedure is to empty the tank then START THE SAW and let it run until it dies. If you do not do this, ESPECIALLY with ethanol gas, you are asking for the carbs to get varnished when the gas goes bad. At that point, a professional cleaning is likely and a complete parts replacement of the carb parts may be in order to get it back into proper running condition.
Higher octane gas doesn't do a thing for you. The octane is higher, so it should take longer before the gas deteriorates below the minimum required rating for the saw. BUT... "Super Unleaded" fuel sits in the tanks at the stations MUCH longer than 87, so it's shelf life is much shorter.
Use a quality fuel stabilizer for ethanol gas, a little SeaFoam now and again isn't going to hurt, and a quality 2 cycle oil. Drank the fuel reservoir on the saw and run it dry before putting it away.
For starting, the steps have been outlined numerous times: full choke pull until it fires once, half choke until it starts. When it's warm, simply throw it to the "on" position and pull. If it won't start in the "on" position, repeat the process.
The MS-290 is about the hardest starting saw they have because it's the biggest motor that doesn't use the decompression option. My 290 starts within three pulls EVERY TIME unless I somehow flood it. Even then, no more than six.
FWIW: It needs a legitimate pull. I use the "hold in right hand, grab pull cord handle in left, hold tight, and throw saw toward ground while pulling up on starter cord" method.
