thank you, I spend some time this afternoon going over the crank shaft with a file. I re tapped the starter cup (witch includes the aluminium nut) by turning it one to another crankshaft secured on a vice using a lot of leverage. This worked for me well. This occurred this morning when I went to start it to test the backfiring. the cup was not on tight by the looks of things and became loose and bored the thread. all good now thank you for you help.
