What should I do? Merc 650 Thunderbolt

What should I do about this motor first to get it running? I have already made sure the fly-wheel turns and the driveshaft also. Anything I should check before I try and start it up... Boat and motor sat in the woods for 5-6 years before I took it on recently after the former owner gave it to me. It was profesionally winterized when it was put away and there was water noted in the gear oil. I am only 14 and I dont have that much money to replace or have a lower unit seal job done right now. I would just like to get it running, and I have worked on smaller motors (2hp Honda and 4hp Johnson) (dinghy motors)

It is a Mercury 650 (65hp) 4 cylinder 2-stroke

Is there anything I should check or inspect before the momment of truth?





Thanks, Adam

Re: What should I do? Merc 650 Thunderbolt

borrow/buy a compression gauge and check compression on each cylinder, make or buy a spark gap tester to see if you are getting spark on each cylinder. spark needs to jump a 7/16" gap. spray some 2 stroke oil in the spark plug holes and hold the carbs open and spray some in the carbs.

Re: What should I do? Merc 650 Thunderbolt

The engine appears to be a 1969 650 based on the colors of the wrap.A serial number would help confirm that.The plugs are surface gap plugs in that case.
As mentioned before a compression check would probably be your best place to start.Ron G

Re: What should I do? Merc 650 Thunderbolt

That motor looks fantastic! If you lived near me I'd check it out for you. Check all the wires for cracked insulation and shorting (the wire at the top of the green square thing looks rusty) tilt engine up all the way and pump clean gas into the motor, and see if it leaks out of the carbs.
If fuel comes out return motor to level and see if pump bulb stays hard.
Buy a flush tester, connect to garden hose and put it on the lower unit water inlets.
To start motor raise the small lever on the control box to 90* angle-turn key and press the black choke button and hold while turning key to the right.

Re: What should I do? Merc 650 Thunderbolt

Rebuild the water pump, or at least replace the impeller. That old impeller has most likely taken a 'set' and will not provide proper cooling at speed, why risk overheating that fine old motor?

Re: What should I do? Merc 650 Thunderbolt

Looks like a 69 model like mine:

1) check compression and spark like sparkie above said

2) I would try running it but only for a short period of time on mouse ears or in a barrel of water as the impeller is probably shot and wont pump very good use 50:1 oil/gas ( i use pennzoil 2 cycle semi synthetic in boat section at walmart)

3) The lower end shaft is mild steel and will rust if not taken care of, my top splines were pretty worn from lack of grease and rust, when the time comes to change impeller make sure to grease splines.

4) these engines need a good battery with a good charge to keep them running as the capacitors are charged with battery power to fire the plugs make sure the charging system puts out before going on any long adventures.

5) looks like everything is there including tilt trim they run real good when working right its just the initial steps like oil mix and watercooling to keep it that way.