Do a search on the net for tuning information on older 2 stroke motorcycles. I doubt that you'll find exhausts for an LJ50, you can probably rig up an electronic ignition. Has the LJ got fixed ignition or an auto retard? Usually mod for older 2 strokes is to skim the head to bring up the CR a bit and to get the squish band just right. You could clean up the porting but I'd be wary of lifting the exhaust port height as you will lose bottom end power. Nat Ham on difflock.com has an LJ50, he's just rebuilt his engine and by all acounts it does very well.
