Mercury outboard long shaft 20HP. Needs lower impeller replaced. Run excellent and other wise in great shape. Selling to purchase anew one. Make a reasonable offer.

You posted that it stops running, but will restart. You also post that it has a bad water pump impeller. Together I hear "overheating". I may well be wrong, but it may explain the lack of responses?

Either not such a "hot" motor, or not such a hot ad...

The motor does over heat due to the lower impeller stops pumping water. Replacing the impeller will fix the problem.

Here's what happens when a motor overheats. Not busting your chops, just letting you know. The pistons expand and eventually the rings drag on the cylinder walls enough to stop the engine. The engine will turn over again as soon as it cools, but the rings, because of their tight contact with the cylinder walls can lose their temper. This causes them to wear out more quickly, and you end up with a "smoker". There can also be scouring of the cylinder walls and premature failure of the crankshaft and rod bearings due to the excessive drag while in the process of seizing. The waterpump impeller can be replaced all right and will pump water and cool the engine, but the amount of damage done to the engine prior to repair is "iffy" at best. Sorry.

Don't be sorry good feed back. I will just junk it and purchase another one.