Seem to have a fault with my WR400, bought as a non runner project. Unable to obtain a tick over/ hard to start. Have had the carb cleaned untrasonic checked all the jets for size and blockage all seem ok. Removed the head re-worked the valve and rings hence good compression. I can only get it to run with the tick over screw wound in as far as poss this will give me an idle provided the pilot air screw is wound well out, but as soon as I use the throttle it just dies. Have moved needle jet up and down this gives me a clean throttle resonce up the range but nothing down low. any idea? Will a different carb fit to try?