Hi, by memory--[used to work for a yam dealer a lifetime ago] SR500 Yams are 12volt cdi or tci so just saying be careful what you buy. If it's the original system it'll only have the trigger coil only down the bottom, i think it's sitting outboard of the flywheel activated by a raised strip on the flywheel. XT/TT250's are cdi & don't get me started on 'that'--they used to stuff the box & stay fully retarded [barely run--idled good lol], had one [still got it] guy bought to me with the exact symptoms--cdi box i said, so to prove a point before spending lots on a box i advanced the flywheel & did it up bloody tight minus the key which helped but didn't fix it and found [after head scratching] that the inlet cam lobe had all bit disappeared [i mean gonnne]. Went good after that lol. Sorry--getting off track again.
