230E Hard Starts When Engine is hot

[tailgunner]

Hello, IŽd appreciate if someone gives me a hint:
my car starts perfectly when cold and runs smoothly, but when the engine is hot i have to crank the engine at least three times before it finally starts, i have changed fuel filter, spark plugs, cables and made a tune up but the problem remains the same....the car can be parked for 1 week and starts at the first crank, but then the Žproblem appears when i run the engine for a while....from time to time it starts when hot, but is not a regular case.
thanks for your replies