07 WR450, just finished rebuilding. Bike has new camchain,HC piston, rings, valves, springs and head was flow ported. Timing is good, quadrupled checked, valve clearances good, and bike has good compression, ring gaps are in spec and orientated correctly. As far as carb work I raised the needle a clip, didn't touch slide, put in a new needle jet emulsion tube, new richer pilot and main. I also removed the fuel screw, couldn't find theold washer and oring, so added one I had from an old fuel screw. There could possibly be 2 in there...... Floats are good and I can blow unrestricted through all vent tubes and fuel intake with floats open. I'm getting a squirt on the acelerator pump when wicking the throttle. Problem is I can kick and kick and kick, get the odd backfire but when I check the plug it's bone dry. Spark is good. It also seems to be some kind of blockage for fuel entering the carb, like it makes a vapour lock. When I tip the bike it seems to take longer and have less flow from the overflow. And then when I disconect the fuel line at the carb it's only less than half full, like it can't get fuel. I've tried 2 different petcocks, and fuel lines. When I turn on the petcock from the tank disconected from the carb it runs freely...... And no, there is not a rag in the intake or exhaust Any ideas out there????