Hi Bruce, I thought I would let you know that you were spot on with the muffler. grin I soaked it in brake fluid at the advice of my brother (mechanic) and then used the blow torch to burn the carbon off. I have cleaned up around the exhaust port and all and finally got it all back together about lunch time today, after taking mum and the kids to Maccas for Mums Day brekky. Started it up and for 10 minutes it ran beautiful and then started backfiring and spitting out debris, obviously carbon. Once that cleared it settled down and ran for a few hours while I caught up with the mowing. Would have finished the whole block but rolled the deck belt when it got clogged in the long grass.
Off to Mt Isa tomorrow (driving) so will fit a new belt next weekend and finish off. Thanks again for the quick diagnosis and have a great week. cheers Gazza