Back to Basics
We had an MH27I (Delphi fuel system) that was running rough and surging at idling. The mower was sitting outside and hadn't been started in about 8 months. We drained the fuel and added some fresh fuel, but found very little change. Adjusted the governor and initialized the TPS and the unit got no better, so I figured I let it run for a while and see if anything changes. After about 5 minutes of running, the engine puffed out a large cloud of white smoke, shut off and would not restart, also there was a strong fuel smell. I took the dipstick out and smelled the oil, it smelled like fuel as well. So I figured if the machine is not blowing black smoke (rich condition) how is the fuel getting inside the engine? On the new EFI engines there is a low-pressure fuel pump mounted on the valve cover. I remembered there is a diaphragm inside the low-pressure fuel pump that could get damaged due to bad fuel. We took the valve cover off and took the fuel pump apart and found the diaphragm had cracked and fuel was leaking though and going in to the sump. I replaced the low-pressure fuel pump and it took care of all the running issues.
Moral of the story. We can be quick at blaming the EFI system for erratic running conditions, but sometimes we need to go back to basics in order to fix the engines.