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I have a briggs v twin on my husquvarna mower and it will start up but when i try to throttle up is acts like it is starving for fuel and starts poping back through the carb. I have rebuilt the carbs and cleaned them twice. I also cleaned the heads and valves installed new gaskets. When i set the valve lash to the spec the starter wont turn the motor over any ideas need help please.

First off let me be the first to say "we need your Name, Rank, and Horsepower! (Model, Type, and Code) of your engine"

Recheck your valve clearance, make sure you set them when you are slightly pasted TDC.