Backfiring is an indication of lean mixture (not enough gas). First thing to do is make sure you don't have any leaks in the exhaust system at the head pipe or the muffler joint that could be pulling in cool air and contributing to the back firing. Second thing is you want to make sure the air jet passages in the back of the carb are clean and the pilot jet is not partially blocked. Third is, assuming step 1 and 2 are ok, put in some fresh high octane gas and richen up the pilot jet.
Adjustment might not help. Sounds like the needle valve has to be changed. Might not be seating properly and therefor flooding the engine.
If it starts and dies after a very short while, look for a fouled spark plug (flooding), clogged fuel filter (fuel starvation), clogged air filter (flooding), or fuel settings on the carburetor (flooding or fuel starvation).
Float probably stuck or has a hole in it allowing fuel to enter or Bad needle and seat valve
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Have you checked to see if the float has a hole in it allowing fuel to weight it down? Possibly the needle valve is sticking and not the float. Could also be the float needs adjusting. You need to open the carburetor up and see what is going on.
Sounds like it is flooding out. Try idling your carburetor up. unless it is fuel injected. also use some carburetor cleaner, or throttle body and injection cleaner if its fuel injected.
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a flooded carburetor will spill fuel into the combustion chamber causing an improper fuel to air mixture. too much fuel in the combustion chamber will not completely burn. the unburned fuel will be pushed out of the exhaust.
There are several things that would cause the engine to flood and not ignite. If you haven't used the blower in over a month, the fuel may have gone bad, thereby not igniting and flooding the engine. The carburetor float may be stuck open and not stopping the flow of fuel when full. The carburetor needle valve(s) may need to be adjusted - sometimes the vibration of the engine will cause it/them to close or open.