This is my first post and I hope someone can help me. I have a Ditch Witch backhoe that has a Deutz F2L511 air cooled engine in it. It always starts, but blows black smoke and then slowly dies after 5 minutes. The injector pump has an "extra fuel solenoid" that pushes a pin down at cranking. The pin is supposed to stay depressed until the engine is at a high RPM and then push back out. This is not happening. Last year it did this and then it fixed itself. The injector lines both are getting fuel but the mixture seems messed up. What I find strange is black smoke means too much fuel but it acts like it starves after 5 minutes. I changed the lift pump, fuel filter, checked the fuel separator and blew the fuel tank lines out. Any suggestions would be appreciated.