Need some help guys. I have a 2009 Kawasaki KX 450 F. All valves are in spec according to manual. Fuel pressure is good according to manual. Timing is exactly where manual says it should be. Will only start with starter fluid and then backfires. I thought it was the fuel injector so I purchased a new one and same symptoms. Also put a new fuel pump on and still the same symptoms. Any ideas on what it could be and where to go from here.