Hard Starting 23 Hp Kawi

HI GANG I HAVE A QUESTION ,I HAVE A BOBCAT ZTR 218 WITH A 23 HP KAWI.TH E PROBLEM IS AFTER THE MOWER RUNS A WHILE IT HAS A HARD TIME STARTING WHEN HOT , IT STARTS FINE WHEN COLD. WHEN IT WONT START I PUT A NEW SET OF PLUGS THEN IT WORKS FINE. THE PLUGS ARE CLEAN AND WHITE. I REPLACED ONE COIL , DO YOU THINK IT A COIL PROBLEM. SORRY FOR THE LONG POST. THANKS GUYS