Most carbureted bikes will exhibit some amount of popping on deceleration, especially when the throttle is completely closed. While mild popping is not objectionable, serious popping can be very annoying and symptom of a fuel or exhaust problem.
Decel popping occurs during a temporary lean fuel mixture condition. This usually happens when the throttle is closed quickly after wide opening. This can be caused by a lean idle mixture or an air leak in the exhaust.
Exhaust leak Edit
A simple fix is to make certain there are no holes in the header pipe or remaining exhaust. Secure all mounting bolts to eliminate any possible gaps. These holes or gaps allow air to enter when pressure in the exhaust is low allowing unburnt fuel to combust in the exhaust.
Be careful when removing rusted or seized exhaust bolts, they are easily broken or damaged. It's best to apply a penetrating oil. Some well known oils such as PB Blaster or Liquid wrench are known to work. Kroil has been highly recommended by some, but is only available online.
Idle mixture Edit
If there are no exhaust leaks, enrichening the idle mixture can help. Adjust the idle mixture screw slightly as needed.