Did the tank get jostled at all when you removed it, or put it back on. The reason I am asking is: on Sunday of last week I helped a friend with a GSX-R 600 that wouldn't start. We removed the tank, airbox, plugs, fuel rail, fuel injectors, and fuel pump to test everything. We replaced the plugs, and tested for spark at each plug, checked compression on each cylinder, checked the fuel filters in the injectors and cleaned the filter and injector nozzle. Then put the plugs, injectors and fuel rail back on the bike. When we pulled the fuel pump out of the tank and looked in the tank (tank was upside down) I noticed a couple of parts in the tank that were just sitting in the remnants of the fuel. I grabbed them with a part puller and it turned out to be the check valve and retention clip of the fuel pump that had come off. We cleaned everything up and re-attached the valve and clip to the fuel pump. Put the airbox back on. then the tank and fueled it up. The bike fired up immediately. he said that before it wouldn't start at all the bike had serious lack of power issues like it wasn't getting fuel at higher revs. Then all of a sudden it wouldn't start. We think that the check valve was loose on the pump causing low fuel pressure which higher revs demand.
Just a thought,
~D~