I have seen bad gas do many things, from stalling the motor when you try to open the throttle to chugging and stalling, to just not allowing the motor to start at all.
As stated, remove the bad gas and replace it with fresh stuff. If your on the road and happen to fill up with bad gas, sometimes a bottle of gas treatment will get you through that tank and not leave you stranded.
I always try to buy from national brand gas stations to reduce the risk of getting cheap or stail gas.