"Drain the gas and replace wit
"Drain the gas and replace with new. Be sure to flush out the supply lines to and from the VRO as well. Also, empty the VRO tank and fill with fresh oil.
Purchase carb rebuild kits, remove the carbs, flush, clear out, and soak all parts with carburetor cleaner using compressed air to blow through all orifices. Remove all jets and be sure they are completely clear of any debris or varnish. Reassemble using new needle valve and float. Now would also be a good time to replace all the fuel hose on the engine.
Drop the lower unit and at minimum install a new impeller if not the entire pump assembly. I had a neighbor that bought a boat with a Merc 20HP that had set for several years. The first time he took it out the engine overheated. He got back to the house only to find the impeller fins had scattered into a 1000 pieces and we had to repeatedly backflush the cooling lines to get all the little rubber chunks out of the engine.
You might consider replacing the thermostat (is there more than one on this engine?) just in case it is corroded shut.
Throw a new battery in the boat and ensure it is fully charged. Remove the plugs and spray some fogging oil in each of the cylinders. Then, while cranking the engine (with the plugs removed) spray some fogging oil in each of the carb throats. Rig up a spark tester and ensure that you have strong spark to each plug. When this is done, install new plugs.
Finally, just to be on the safe side, I would add some oil to the fuel tank (25:1 and maybe 5 gallons of fuel) to ensure you're getting some lubrication to the engine. I'm not familiar with VRO's but if something is bad on it you could quickly toast this engine. Once you've confirmed the VRO is operating properly, then you can fill the tank the rest of the way with straight gas and the little bit of oil left will be no problem at all.
Lube the tilt tube, run tilt/trim all the way up, remove the fill screw and make sure the reservoir is full then run through it's entire range a couple of times, check forward/reverse engage, and turn completely left and right to see if steering cable is ok. Fire it up on a hose to be sure everything is operating fine and once all is well, head to the lake and have some fune.
KJ"