The mighty GR650 Tempter worth saving
I never had one, but I've admired these bikes. Cycle evaluated one in the early eighties and found nothing much to dislike except the name. The bike was good for commuting and touring and got nearly 70 mpg if memory serves. There was one unusual feature of the bike--it had a clutch of some sort that brought a heavier flywheel in at low revs and then disengaged to free the engine of excess inertia at higher revs.
You may be able to fix this thing for very little $ if you can do all the labor yourself. The bike will never be worth much, but it could be a very nice commuter or touring bike.