When I carried my motor (and boat) in for servicing, It ran great. When I got it back 2 cylinders appear to be starved for fuel/air. The dealer says it is getting fire but 2 injectors appear not to be working. All he supposedly did was replace plugs , gear oil, and grease fittings but now even with the analyzer, he cannot figure out how to fix it. What are the possible causes of this? Thank you for input.