I just bought a new '05 kfx 400 to replace my '03 z400. I swapped my hmf pipe and K&n filters over to the new one, jetted it in, runs great but I have to have the fuel valve in the "prime" position to run now. At first it wouldn't stay running and after much frustration I went to the HMF web forums, and an employee there wrote you have to run it in the "Prime" mode, because there isn't enough vacume to actuate the check valve properly. My '03 didn't have this problem. Does anybody know if it's a different valve, or because the new carburator is 1 mm bigger?

 

My 2005 model doesn't do that and its got all the mods listed in my sig.

 

I think that since the carb is bigger, it needs the jets to be a little more open as well to feed the engine. If you get a jetkit for the 05 model, it will run fine.

 

It is jetted for the quad w/ kn power lid and kn filter and outer wears and hmf pipe, 27.5 pilot jet, and 160 main jet, a/f screw 2.5 turns out. Maybe the fuel valve itself is bad? I hate to drive it out to the dealer for them to have it 2 weeks and tell me it's fine. It is still under warranty, but they might not cooperate seeing that it didn't have this problem in stock form.