When I start my nitro engine it runs fine, but when i break the engine quits. I have checked the carb and when i break there is still a gap. When i break the gap of the carb is the same size as when i am idling.

Have a look at your clutch and see if it is locking up

If you idle gap is set correctly then it sounds like your clutch bearings have gone. This will not let the clutch bell spin freely so when you are breaking the bad bearings are grabbing instead of spinning and stalling your engine.

+1 check your idle gap when your brakes are applied. Sounds like your servo may be slightly holding the throttle open when at neutral, then when you hit your brakes the pressure from the spring closes the slide. Easy fix happened to me a few times.

Yep......