I buy and service a lot of bikes, and have never seen before the types of fuel problems I am now encountering from people leaving untreated (un-stabilized) ethanol gas in their tank for extended periods. Untreated, it has a very short tank life, experiences "phase separation" in about three months, then burns poorly and the alcohol content corrodes and clogs the carb jets and injectors. This isn't my opinion either....it is a fact that you can research all over the web on many professional repair forums. Untreated ethanol gas left in your bike, ATV, mower, weedeater, rototiller, tractor, occasional driver car etc. will cause problems, and generally sooner rather than later now, often requiring a complete carb overhaul and/or system cleaning. And "starting the bike every few weeks" may help a little, but it doesn't address the root problem....your gas now goes bad quickly, can easily clog things up and cause numerous running problems
I personally use either Startron, Stabil for Ethanol or Lucas stabilizer in every tank full, and the add Lucas fuel injection cleaner (condensed cleaner) in the recommended dosage in every other tank to keep things clean. If you can find non-ethanol (recreational gas) anywhere locally, that is the way to go, especially during winter lay-up. Once the gas has turned, usually int three months, you should drain and refill with the above mixture or maybe B12 Chemtool instead of the Lucas injection cleaner, and do this for a coupe of tank fulls. Ethanol isn't your friend and a new routine for gas treatment in our bikes is now required.
When I am buying bikes, my first question is: have you been using fuel system stabilizer, and if so what kind? Next, do you keep your bike on a tender? Third, has your bike stored dry and indoors? No stabilizer is worse than the wrong stabilizer (wrong is like Marvel Mystery Oil or conventional Sta-bil that won't treat ethanol). A bike stored without being on a tender will have a battery life of only 1-2 years, on a tender, almost indefinitely. A bike stored outdoors, even under a cover will (generally) experience much more rust, corrosion, oxidation and deterioration. As a buyer, I make deductions for all of these things.