Fuel issue?
 

Installed a 440 kit in my buddys z400. 2004. Ran fine after install and that's it. Now it won't start. It will bump start. It won't start on it's own. Completely tore the carb apart and cleaned it. It's jetting fuel to.l the carb from the tank and to the bowl. InsTalled a new plug also. I tried to purposely flood it out and the plug never gets wet. Should it? Doesn't seem like it's getting any fuel to the motor but if i bump it it runs. So it has to be getting fuel I would think. It also ran fine before installing the 440 and besides a new clutch that's all that was done.

Have your valves closed up? If valve clearance is too tight they get bad to start.

Pyro here. I've had this problem before.
When hopping up a stock motor, more load is placed on the starter.
This is a common problem on Harleys.
If you go to the factory spec's they may tell you what kilowatt starter you have.
A good starter,alternator & generator shop can rewind your starter to a higher KW.

If it's not spinning sufficiently fast to turn it over you may get away with a better battery that provides more CCA