SS14 BRIGGS BACKFIRE THRU CARBURETOR WONT START

I just got a SS14 with Briggs engine. Cant find model or serial number. The problem i have with it is when i try to crank it it wants to backfire thru the carb. I have cleaned the carb good. I have got it to hit for a few seconds but dies by adjusting inlet and idle needles. Could it be an intake valve leak? Want advice before I tear it down. Thanks

Pull the nut from the flywheel and see if the key is sheared or partially sheared.

JW , i don't know anything about B & S engines , if yours has points may try cleaning them with some fine sandpaper and reset the gap , just a thought . if you got it going again let us know what the problem was and fix . > tim

Thanks guys for your input. After the suggestions i pulled the head and found oil (lot of oil) on piston. Rings on order. Let you know if this fixes things.