On my track 3TJ, the CDI had a lump on the front fo the case like someone's been in there and plastic welded it up. Any thoughts as to what it's likely to be? I'll get a picture if it clarifies things.

Sounds like it has been modded to alter the ignition timing and increase HP.

Hi, would need a pic to see what it is.

LOL, CDI is buried under the rear seat bracket & plastics and bike is buried under the workbench, so can;t get at it without major hassle.

Artist's impression is the best I can do. The red circle is raised about 3mm. The red line looks like it's been plastic welded (not really raised). Turns out this bike was a cat C and converted to a track bike. Perhaps it was used as a racebike for a while as it was pared down.