I have an "03" 400ex. My stock engine ran fine just had a little valve tapping. I then blew the piston to pieces. I got all the pieces out of the motor block. So I just put in the Wesco 440kit. Now its making a funny noise when i give it gas, its like a chirping noise. It is also extremely hard to start. I just put new jets in today. My friends and I can't figure out what is wrong. Please help.

 

Chirping indicates a blown head gasket. Check the compression, and see if you can find any marks indicating leakage of fuel or oil round the joint between head and cylinder. Another possibility is the inlet manifold joint. Could just be the exhaust joint, but you wouldn't get hard starting from that leaking.

 

You got to read that spark plug, from what you are telling us you did the work yourself. What is the compression?

Some more info will help.