I've got an older John Deere mower with a kawasaki fc420v engine. Once started, the engine purrs like a kitten at any rpm. I couldn't ask for a smoother running motor. The problem is getting the thing started. It backfires out of the intake and exhaust. It takes 30-45 seconds to get the thing started. I've checked the valve clearances and reset them to spec at .006. The compression release is measuring .027" right after the intake valve closes as specs say it should. The coil is putting out good fire at the plug. I reset the air gap between the coil and flywheel to .012". The valve are sealing off properly. The carburetor has been off and cleaned. I also checked the flywheel key and its in perfect condition. Any ideas on where to go from here?

You may want to check the choke linkage and make sure the choke is closing all the way for cold starts.

I was going to try that today when i get home because I had read that the choke not closing was a common problem with those carburetors. I hope thats it, but it wont start easy when its warm either.