Get an outdrive water intake cover with a hose connection (if you don’t already have one), that fits / closes around the drive’s water intakes on both sides so you can test start it while it’s on the trailer in your driveway.

If it’s been sitting that long, I’d also do the usual stuff, e.g., change the oil, replace the ignition components, and make damn sure that both the blower fan is working, as well as the bilge pump. Don’t run the bilge pump dry though; just turn the switch on/off to see if it starts/stops. If your engine uses Fuel Injection, check the electronics. I was on a 5-boat tripmfrom West Palm Beach tomthe Bahamas, and one of the boats we were with the engine wouldn’t start. My professional background is in Electronics; I was able to trace the problem to a circuit board that regulated something (been nearly 30 years ago). The owner had to have the part flown in from the U.S.; needles to say he wasn’t happy with the guy who checked out his boat before the trip. It was a 30’ I/O, can’t remember the make. He’s a D.C., so he had the $$ for a nice rig. To this day, whenever we see each other (infrequently since we live on opposite coasts), he thanks me for that.

Point is, make sure your Electronics are working; always keep a multimeter aboard. If you don’t know how to use one, learn.

I’d also replace the battery/ batteries. Most marine batteries are designed for a wet environment; depending on the storage conditions (temperature, humidity, etc.) the case could be cracked, connections corroded, etc. The last thing you want is hydrogen gas leaking from a bad battery. In any case, you also don’t want to be on the water and not have the engine start because of a bad battery.

If there’s any leftover fuel, that can be a problem after sitting for that long. If you can siphon the tank to try most of it out and put high octane gas in (to help level out the mix if there’s any old gas left), it’s better to have fresh gas than old, of course. Hopefully you have had stabilizer in the fuel; if not, getting any old fuelmout can be problematic.

If your using an engine with a carburetor instead of fuel injection, the carburetor gaskets are going to be dry, and prone to leaking when gas does get in.

The other thing most people forget about is to make sure the outdrive raise/lower motor is working, put fresh lube grease in the outdrive gears, and to check the outdrive Boot (the seal Boot that goes around the outdrive to prevent water from entering the engine compartment. If it’s been sitting in a hot, dry environment for that long, the Boot might be stiff or even cracked.

Check the engine compartment and under the dash for any mouse droppings; if you see any, check the wiring under the dash if it’s easily accessible. In the engine compartment, check for any nests or seeds that might be in the compartment, or even in the carburetor. The little bastards can get into anything; they’ll chew wires to use the insulation for nest material.

Oh…if it’s been in storage on a trailer and not a warehouse storage rack, don’t forget that the trailer / winch needs maintenance also. I’d replace the tires, grease the hitch and brake, check the springs and weld points for any rust or cracks, etc. If you have a tilt trailer, checknthe tilt latch for any problems. And most importantly, check to make sure your trailer lights are still working when connected to your truck/SUV, etc. Check the chains, hitch lock, etc.

Make sure the winch and cable works also; you can loosen it, unhook it rom the boat eyehook, then pull the cable out to check it for any signs of corrosion. At the very least, get a smooth rag or blue shop towel, soak it with WD-40, and run it along the cable both to lubricate it and prevent corrosion. Also, wear mechanics or garden tool gloves (I use either Stihl or Husqvarna Chainsaw gloves), NOT any cloth or rubber gloves. You want to check for any broken wire strands in the cable, and any wire sticking up will snag on rubber or cloth. Suede/leather is a lot better. Don’t forget to check/spray the winch gears also.

Boat plug; make damn sure that the plug is in the drain hole BEFORE putting the boat in the water. Beforehand, check the plug to see if there’s any dryness/cracking in the rubber outside the plug. Replace it if it shows signs of dryness or cracking.

I know that’s a lot more than what you asked, but having been around boats since I was a baby, things just pop into my head when talking about boats/boat maintenance, and problems over the years without being used. My Dad built boats for many years, from outboards, I/O’s, to jet boats.

Honestly, with everything I’ve mentioned, it would be easier to take it to a good local shop that does boat maintenance. It’ll cost a few hundred, but might be better in the long run if you’re not up to doing everything yourself. Even if the boat was in the water that long, you’d still need to have everything checked. Replace your batteries at any rate;6 years is a long time for a battery to sit uncharged. Also, get some connector pads, and put a penny or 2 (use a bit of Vaseline to put it on) in the center top of the battery. Put the Vaseline on the battery case, then put the penny down into it (leave the top of the penny clean). That’ll act as an anode and help keep the connectors from getting corroded. Works good on car batteries also.