Have a 17 hp b&s on a L100 JD mower that is spitting back through the carburetor after it run about 1 min. have already adjusted the valve to .005 and .006. Hard to start before adjusting cranks great but the spitting continues not as bad before adjusting. Looses power when the blade is engaged and spitting gets worse. Any suggestions?

Most of the Briggs engines the intake and exhaust are adjusted at the same time with the piston 1/4" down on the power stroke.

Does it ever backfire? I think you may need to clean and readjust your carb. Sometimes this won't work and I have had to replace a few carbs that just refused to be cleanable.