Kawasaki Forums - Prarie 650 No Start. Spark and fuel

I'm in the process of rebuilding my buddies 2002 prarie 650. It was overheating and the coolant would boil. So I pulled the engine. Sent the new wiae cpo istons .50 over. And the cylinder and head to the machine shop. I had it bored and flattened due to scoring. I torqued everything to spec, aligned the cam sprockets with the TDC for both cylinders. Finally got the engine back In and tried to fire it. After trying several times I checked the spark plugs, I pulled them, put them on the block and got spark from both of them. Then put some starting fluid in it and tried again. Still nothing. For a split second it sounds like it will start but won't. I didn't touch the valves and left them where they were when it was running. Any ideas on what the problem could be?