my johnson 6 hp seahorse runs ok when i begin trolling with it , but when i run it at wot for a while and then go back to trolling it starts to run on one cylinder ,i checked the spark and i got spark on both cylinders ( did the sparkcheck in my garage , not when it started to run on one cylinder ). and i checked the reed valves seem ok but when i turn the flyweel by hand i notice it blows foam back from gasoline is this normal or should it be perfectly airtight . <br /><br />any suggestions ???