I have already replaced the spark plug wires, ignition coil, fuel filter and fuel pump. These were all replaced a year ago, and resolved the initial stuttering problem. Now the car stutters at about 5200 rmp's. Also after driving around, and letting the car sit for an hour or more, it takes about 10 seconds to start after turning over several times. But, if you let the car sit for an extended period of time, overnight, it will start right away, but black smoke will pour out of the exhaust. Do you think the problem is fuel related, and/or ignition/optispark related?

 

You more than likely have a leaky injector. It can be allowing fuel to puddle in the intake. You have to crank it longer to burn off the excess fuel. After sitting for a longer time, much of it will evaporate. You should do something right away. Smell the oil on the dipstick to see if it smells like fuel. If so change it and fix the problem right away. To check if this could be the problem, put a fuel pressure gage on the fuel rail and see if the pressure drops real fast after the engine is shut down.

If it does drop, pull the fuel rails up with the injectors connected so you can see the nozzles of the injectors. Have someone inside the car cycle KOEO enough times to view each nozzle when the pressure comes up to see if they are dripping.

Also check the vac line to the fuel pressure regulator to see if it is wet.