John Deere L120 motor surging after warm up
John Deere L120 with ~ 150 hours on it. Briggs 20 HP V Twin engine. Regular service at the proper intervals - oil, oil filter, fuel filter, plugs, air filter / pre-cleaner all about 10 hours ago. This just started happening - runs great then after cutting for less than 30 minutes the motor begins to surge as if the choke is engaged. I can get it to run smoothly for less than a minute by giving it full choke, then it dies. If I let it cool it will run OK for less than 15 minutes, then begins to surge again. So far I have tried gumout carb cleaner in the tank and have run about 1/8 of that tank through. I've also tried spraying carb cleaner in the air intake. Any thoughts?