To all you two wheelers, you may find more and better answers to your posts in the Motorcycle Engineering forum. Perhaps there are a few more biker types there, too.
Tigs here (Katana 550). The simplest ideas are the best - I now have the Motorcycle Forum on my list of forums to visit - thank.
IN case your interested, I've replaced the faulty coil on my 550cc Katana and it backfires all over the place (and yes, I have reversed the HT leads, but it makes no difference - strange but true.
Thanks for all your input regarding the Katana. Tigs