OK you asked for it.
No point in spending money or time on motor if compression is bad, so check it first (make sure the battery is strong and squirt in a bit of 2 stroke oil to lubricate the cylinders). You just want all the readings to be consistent (within about 15% of each other) don't worry about the actual values because they can be misleading.
Then get a service manual, best money you will ever spend if your serious about getting the engine up a running properly and safely, and you will learn lots along the way.
Then following the manual
Replace the impeller <--------------, this is a must do, no matter how good the old one looks, replace it now and every 2 years from now, and never run or crank the engine without water supply. No point in doing all the work and spending the money just to melt your engine on it's 1st trip out. A few bucks is all it takes.
Rebuild the carbs with service kits.
Replace the gear oil.
Change plugs making sure to use the correct ones, given a choice go with NGK.
Check carbs are properly linked (all open at the same time and by the same amount)
Check carbs and ignition timing are synched (following the manual) and of course that you have spark.
Grease everything that needs greasing.
Got trim and tilt, check it works
Change all the fuel lines, from tank to engine. including primer bulb. with ethanol resistant lines. (old fuel lines can clog your nice clean carbs and ruin your day real fast)
Should be good to go.
