2002 DF140 fuel in exhaust water

Just got the boat back from the shop for a new high pressure pump and regulator. They also replaced the thermostat and removed and cleaned the injectors at the same time. Launched the boat and smelled fuel but thought it was from an overflow while filling. At the dock idling, there was a large rainbow coming from the motor along with a strong fuel smell. Put the boat back on the trailer and ran it on the muffs. No fuel or oil coming from exhaust relief but when I put a bucket under the prop to catch the water, you can see the fuel laying on top. Checked the plugs and three were carboned up pretty good and the number two was wet. I called my dealer and returned the boat for them to fix. Any idea what they could have done or not done to cause this? The engine ran great and achieved full rpms when I took it to the ramp.