I had the same problem on an old O.S engine of mine where when i applied the brakes it would cut off the engine because the carb linkage would not stop goin back (rotary carb). I kept having to adjust the idle needle. It seemed if i tightened it all the way down then the carb would not go past that resting point. i.e when the brakes are applied. But that was my case. not sure if yours is the same.