dont know about ur XR2-200 but with my 1976 Merc 500 50hp ( have had it from new ) for years now I put
Quicksilver Fuel system Treatment & Stabilizer in whatever fuel I have left & run it thro the engine usually around now & leave the engine etc until Easter, then clean the plugs & the engine starts on the 1st or 2nd pull ( manual start ), have had no problems since I started using the "stabilizer", not bad for an old timer !!!