So I just traded for a 2001 400ex, I bought a new carb and put a 42 pilot jet and 155 main jet in it. It has. Lexx slip on exhaust and a uni air filter. After installing these new jets, I started it and it idled and ran good. But after riding it for a little bit, it died while I was riding. I had to use full choke for it to start and hiccup my way home, having to start it again every 50-100 feet. It was running fine when I started the ride, now it won't start without choke and giving it gas, but it immediately dies. any help is appreciated!

 

Pull the fuel line from the carb and see if you're getting fuel in the on position and reserve position. If you're getting fuel possible stopped up carb jets,needle and seat problem,water in the fuel,etc.