I RECENTLY SOLD A SCOTTS RIDER WITH THE 18 HP OHV BRIGGS ENGINE. THE BUYER BROUGHT IT BACK AND SAID THAT IT STATTED SMOKING AND MISSING SO I ASSUMED THAT IT HAD BLOWN THE NEW HEAD GASKET THAT I HAD INSTALLED. I CHECKED TOE DIPSTICK TO SEE HOW MUCH OIL IT HAD AND IT SMELLED LIKE GAS AND WHEN I PULLED THE HEAD THERE WAS RAW GAS IN THE CYLINDER. IS THERE ANY OTHER WAY FOR THIS TO HAPPEN OTHER THAN HIM PUTTING GAS IN THE OIL FILL TUBE ? I CAN'T THINK OF ANOTHER WAY FOR THIS TO HAPPEN. THANKS GUYS.