I'm working on a 4020 LP tractor. The guy I got it from said it only starts one time of day. If you ever kill it , it will not start. He had a bag full of new part he never put on it. Sure enough I crank it , run it about 30 minutes kill it and no start after that. It only turns over. I start looking at it changing the key switch, points and condenser , rotor, cap, coil, plugs and wires all new even a new wiring harness. All theses parts he gave me. Changed the diaphram in the LP regulator. The fuel solinoid is working I hear it click when key is on. Put a rebuilt starter on it turns over fast. Rock the steering wheel when cranking. All that I got it to run great start great no problem about ten starts in a row. Went back about an hour later and it turns over fine but no start. What now?