If the bike has old gas in the tank drain it out - its not worth the couple bucks for the goop thats in the tank flushing thru your nice $2000 carbs. Nothing can restore old gas that has turned to goop.
If you dont know how to get rid of the old gas (do NOT burn it) put it in something like an oil drain pan outside, where it wont fill up with rain - it will evaporate away in a day or so.
If the bike will run follow the directions on the can, one ounce per gallon of gas (650 holds 4.2 gallons, but you could put just one gallon in to start)
If the bike just wont run well enough to ride it, you could try putting straight seafoam in the carbs - you would have to disconnect the fuel line to the carbs, run the bike long enough to drain out the float bowl, then put some cleaner in the fuel line with something like a turkey baster - dont force it in with a lot of pressure, just as much as it takes to fill the bowls (about 2 tablespoons each)
then let it sit over night, with the gas line re-attached, and see how it runs in the morning - if it will run well enough to ride it, then then the cleaner in the tank will continue to flush out the varnish and goop.
Last edited by KCW; 07-04-2019 at 05:51 PM.