kohler engine trouble

I have an older 27hp kohler command pro with new coils and plugs installed in spring 2017. Runs great till heated up then it back fires from the right bank and eventually looses power. When I shut it down and attempt a restart in a few seconds, the right bank makes a popping sound and the engine restarts and runs great for a time, then the problem starts all over again!
It's got me buffalos!
Does anyone have a suggestion? It's really embarassing when on a client's lawn!