If it's accelerating after you trun the radio on, then your throttle linkage is probably messed up. You need to set it to where you carb is as far shut as your idle gap allows, when no throttle is applied.
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And like the other guy said, don't start your engine until you have your radio on, and have made sure everything is responding like it should.
With you engine off,turn on your radio, and take off the air filter and make sure that when you let off the throttle you carb is closing like it should, and when you hit the brakes the carb is not moving any farther closed then it does with no throttle at all. If when you hit the brakes, and then let off the brakes your carb is opening then your throttle linkage is messed up. You carb shouldn't move at all unless you are applying throttle.