My LawnBoy 5277, Serial Number 8322400 has a starting problem. I have changed the spark plug and cleaned the carb. It starts for less than 10-15 seconds and then dies. It seems that it is only getting gas from the choke. This is a re-occurring problem about every 3 years. Previous fixes have been identified as carb cleaning issue, but the current carb is clean. Please advise if you have run across this problem and know the solution. I suspect that the float may be bad. Thanks.