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Hello. My name is Tan.
The popping and backfiring is usually water in the fuel. It can be fuel starvation and timing also. So start with fuel filters. Dump contents of the fuel filter into a clear container. Look for a separation. If you have a separation that is water. Replace filter and run engine. It isn't very likely the timing has changed. Now when was the last time you had the engine tuned up?
Finally if problem continues run the engine on a different fuel source. If runs better the fuel in the fuel tank is contaminated and it will need to be pumped out.
The trim check the battery cable connections at the battery be sure they are clean and tight.
Post back with findings and questions.