Or did I just get lucky? My 12 year old push mower would not start for the first time this spring. (Always treated with sta-bil) I was able to start it after hitting the carburetor bowl with back end of screwdriver. I mixed fresh gas with b12 chemtool and ran this mixture over the summer every week doing 'touch ups' in my yard. Almost every week it would not start until I tapped carburetor and if it did start on its own it would run rough and stall a couple times during use. I then mixed a fresh tank of gas and marvel oil that was my late father's and just let it idle an hour then it sat for a couple weeks. Now it starts and runs perfect without having to tap carburetor.