Engine issue: runs for 3-4 seconds and dies

I'm not a mechanic but I like to learn so I can do things myself. Ran into a problem and hope you guys can help me out. I have a B/S Model 31Q777, Type 0110E1 motor on a 44inch Dixon Ram. Started as usual but when engaging the blades the motor began to surge up and down. Did this until I disengaged the blades then it would come out of it and run smooth. Did this for twenty minutes and then died. Now I can only get it to start and run for 3-4 seconds before dying. I took out the air filters, motor did the same thing. I unhooked the fuel line from the carb and turned the key to check the fuel pump, plenty of fuel. I noticed that the choke linkage was broken--never needed the choke before and I have had this mower for six years--so I held the choke while starting and it ran for much longer. So I decided to replace the choke assembly. Cleaned the carb up and replaced the choke assembly. Motor still just starts and runs for 3-4 seconds and dies. I pulled the float and checked it, guess what, it floats! I'm running out of ideas. I am going to pull the plug and check it to see if it is fouling out as it does burn a bit of oil (as well as an oil leak that I cannot find) and if I have constant spark but other than that I don't know what to do. I would appreciate any ideas or suggestions. Thanks fellas!