No matter if the problem seems big or small, qualified mechanics will always start with these five basic diagnostic checks. Ask about them to make sure they’ve done a thorough and accurate diagnosis.
Visual. Did they notice anything obvious? Ask about water in the bilge, hull damage and condition of the prop.
Fuel. What’s the fuel pressure and quality? Are the filters or tank pickups clogged? Are there any signs of water in the fuel, or other contamination?
Compression. Ask for the compression reading. Is it good? All the cylinders should be within 10 percent of each other.
Spark. How’s the spark? A good, strong spark should be present in every cylinder. Check by removing a spark-plug wire and laying it on the engine block (or other ground). While a partner cranks the engine, you should see a spark jump from the boot.
Lubricants. Ask about the condition of oils, gear lubes and transmission fluid. Did they find any signs of contamination, water, metal shavings or fuel dilution?