Your 1994 mercury outboard motor 200 hp fuel injected 2 stroke sucks the bulb flat when running why?

Sounds like you have a restriction in the fuel pickup in your tank, or in the fuel line between the bulb and the tank. Inspect, clean out, replace if necessary. Or, if you have an air vent in your fuel tank, it could be closed or clogged. Open it and/or clean it.