'71 Chrysler 70 running rough

Bought a VERY cheap boat/motor/trailer last week. Had been sitting a while. Got the '71 Chrysler 70 hp motor started after an hour of messing with it. Fires up immediately now with hot battery. Put it in the water and it ran really rough with a load on it. Died a couple of times. Wouldn't rev high enough to plane the boat so I just ran it slow for about an hour.

Last week I ran it at home and sprayed carb cleaner in it while running it. Lower unit grease had grey look to it....possible water. Drained it and filled with 90 wt. gear oil. Getting good water circulation. Will wait on impellar. Seemed to run a little better. Then noticed fuel leak at tank connection. Bought and installed O-rings....no more leak. Put boat in water. Ran better, but still missing and not enough revs to plane. Motored slow for an hour or so.

May try sea-foam. Also thinking maybe need to pull flywheel and clean points? Maybe change plugs? Whaddaya think?

Also...and recommendations about what to add to the alcohol-laced fuel we have to buy in order to keep engine damage to a minimum?

Re: '71 Chrysler 70 running rough

Anytime I bring home a used outboard, I ALWAYS check and clean the points, clean and service the carb, replace plugs, change impeller, Check compression (this is actually the first thing I do to see if it is worth the other parts) Lubricate linkages.

This way I know what I am working with and have also gotten familiar with the workings of the engine.

Running a 2 stoke that does not perform properly for any amount of time is a nono. If it is running poorly because it is sucking air and you keep going at any speed you can kiss your pistons good bye.

I would start by pulling the carb and rebuilding it, and also make sure that the timing advance is operating like it should.

How is the spark?

Re: '71 Chrysler 70 running rough

Setting for lomg times? The carbs probably need to be cleaned.
The fuel/oil evaporates and usually cloggs the low/high speed jets.
The air screws should be set at 1 turn out for initial settings.

Re: '71 Chrysler 70 running rough

Assume that everything that can be out of adjustment IS out of adjustment. Change the water pump impeller, the fuel pump diaphragm and gasket, and the lower unit oil.

Never run carb cleaner through a 2 cycle engine. It won't help and may even damage the engine because it does not contain oil.

Remove all three carbs, disassemble them and clean by hand. Do not poke wire into any orifices as they are metered and the wire may damage them.

Buy a manual.