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I'd go on a limb saying this popping might not be a carburetor issue. That's all I am saying.

My 1300 used to pop a bit on deceleration. I removed the USA spec air system from the top of the cam covers and fitted the uk spec coverplates.
Coincidentally this also stopped it from banging out of the exhaust.

McZee raises an interesting point. There are too many configurations, set-ups and variables to account for. That's why I have to "stay-put" on the explanation.