I have a 12.5 overhead valve Briggs and Stratton that had a Nikki carburetor on it and every year I had to rebuild the carburetor because it kept dumping gas into the cylinder so I found a Walbro carburetor off the same model motor to replace it with since I've had good luck with them in the past. I rebuilt the walbro and installed but now the motor pop's and backfires like crazy. Ran great with the nikki just before that and I have no idea what is going on. I checked the timing, timing key, and valve clearance several times but it's still doing it. Any help is greatly appreciated.
