Briggs and Stratton 19.5 hp engine. Blows fuel out the intake when trying to start, never starts. Have taken the carb apart 2 times and cleaned, no change. It do believe it has a bad decompression valve (it locks up when trying to start and I have to block off intake with a piece of carboard to "reset" it). My question is if the decompression valve is bad, could it be enough to blow fuel back out the intake valve? Should I start with fixing the decompression valve or new carb? Thanks,