Ok well a few weeks ago my z400 began to act up. When i first start it if i barely push down the throttle it'll shut off. After it finally is able to warm up when i push the throttle and work it a little bit to get it up past it itll run fine. But at a little bit of throttle it'll usually shut off. Well i took it out for a ride to a little sandpit down the road from my house. Well the throttle started sticking but it if you revd it up a little it would go back to normal. Then that stoped working. Well i kept driving it around the sandpit and out of no where it shut off and sounded like a starter when it dis engages. There was somebody out there who said it wasnt getting spark. My friend started to pull me back to my house down the road so i figured i would dump the clutch and see if it started. It didnt work. Got back to my friends house and it fired right up but stuck at about 3/4 throttle. Stoped on the side of the road on the wayback to my house. when i started it back up it ran fine like it allways used to. I have no idea what caused it and i'm afraid it'll happen again. Does anyone know what could have caused this and how to fix it. Oh and by the way this thing is completely stock. sorry about the lengthy and not so well written problem

 

clean out your carb, and clean it good clean all the passages.. clean your air fliter also... that would be a good start..

 

I drove it around the block and it seemed like it was running pretty well but it started cutting out like it was out of gas. It was dark so i couldnt check. Ill do what you recomended and I'll tell you how it goes

 

Does the overflow on the bottom of the carb ever leak? This sounds like the same exact problem my brother had with his. The needle valve assembly was the culprit. I took the carb totally apart and cleaned everything I could possibly get to with Berryman's B-12 Chemtool. I found out that the o-ring that seals the sides of the needle valve assembly was worn/damaged allowing fuel to leak past it. I replaced that and it runs like new again.

 

Well i've been driving it round my neigborhood and its running fine now. It's pretty odd. No it never really leaks except when i pulling 60+mph wheelies

 

If you were really doing 60+ mph wheelies you would never notice it leaking. But anyway glad it's running good again.