A while back I went through the starter drivetrain gearing... part number by part number. They match for all years including the XS2. My 80 SG starter and drivetrain is identical to yours. They should work just fine without the decompressor.... they do on the rest of 'em.I've never had it hooked up. In fact the cable was removed before I bought the bike. I remember asking my brother why the cable was missing when I bought the bike from him. He said that the local Yamaha shop said it wasn't needed. The bikes started better without it. The E-start has always worked fine. I was going to ask you if you had tried yours without it.