half an hour is a long time.. it's well past the point where a dirty carb or fuel delivery problem will make itself evident.. and it's way past the point where the engine has reached it's normal operating temperature and all parts have expanded to their max from heat..
This assumes that there's nothing special or different about the last part of the ride (like a long uphill climb or something).
I doubt that it has trouble at exactly every half hour.. If the problem happens at variable times, it could be electrical. Check for loose wires and connectors.. Check for worn insulation.. bare wires that are able to touch something on the frame. Look everywhere, including under plastic ties that gather wires together and secure them.
Why spraying carb cleaner on the carb would have any effect doesn't make a lot of sense, unless some mechanical thing on the carb was sticking. (or are you moving some wires or something to get to the carb in order to spray it? )
It might help track it down if the next time it happens, carefully get off the bike without disturbing anything.. take a close look at it and you may spot something thats out of order..