Motorcycle Repair: fuel or spark, fuel line hose, vac line

Question
Ok. i have recently put new plugs and muffle. and cleaned the carbs twice and filter. and petcock. Cleaned them all. My question is, that when i start my 1990 Ninja ZX600R motorC3 it runs like a champ.. but after it warms up alittle it starts to stall and sputter. And when i cut it off and start it right back up.. its hard to start, But i can wait for awhile. It starts right up and runs great again?

Answer
It sounds like you are running out of fuel.This carb set up has a vaccum port hooked to the back of the petcock and turns the fuel on once the engine is running.Make sure the vac line is connected and the pick up screen in the bottom of the tank on the petcock stand tube is clean. If you can try a remote fuel tank and line into the carbs.Plug the vac port on carb or pinch the vac line shut run an extrs fuel line to carbs try to start the bike if it continues to run without dying or sputtering out you have narrowed down the problem. Also you can test the petcock pull a vaccum on the back port fitting and fuel should run into a cup at the end of the fuel line hose. If it does'nt the packing inside the valve could be in wrong or the pickup tube with the screen on it is plugged.