I have a boat that I run for work. I am down and can't run it for regulation reasons because the port engine is producing a slick of unburned fuel. It is not a lot of fuel but even the small amount creates a highly visible slick that has shut my operation down. I have been trouble shooting for a few days and I am stumped, so is my local mechanic, and even Yamaha. Here are the clues:
- 2013 350HP Yamaha F350XCB (pair, port engine is the one creating the slick)
- Engine performance excellent
- Smell a little raw fuel from exhaust
- Slick produced by bubbles coming up from exhaust coming out of hub. Can see the fuel slick produced behind boat at idle speed as bubbles hit surface (see attached photo)
- Also get slick when flushing engine- presumably flushing out unburned fuel from exhaust
- I put an oil boom around the engines and when I run the port engine it contains the fuel slick. After 10 minutes or so it evaporates off- confirming my assessment that it is fuel and not oil.
- No fuel in cooling water coming from pee stream (collected it)
- Yamaha Diagnostic Software detects NO problems- no bad sensors, no codes, injectors are all firing etc.
- I dropped one cylinder at a time by disconnecting the coil and all cylinders responded exactly the same- indicating no problem with spark.
- I swapped all injectors from Starboard engine and problem did not go away- not and injector problem
- No fuel in oil
- I pressure tested and swapped the vapor canister and check valve- did not fix the problem - not the vapor canister
- I tried to do a compression test on Friday but my 14mm tester wouldn't thread in so I am going to try that today, but given the scenario I am not expecting the compression to be off.
