Internal dimensions?

[Ward P]

It accelerates and runs smoothly, but farts and backfires heaps on decel.

Apart from jetting etc. type issues, that could be just air leaking into the inlet/exhaust system on the over-run. Old rubber boots and the like on the inlet or poor sealing on the exhaust side.

Thanks, just checked and exhaust has some movement. I'll pull it down to clean today and give it all a visual. - then stick up a couple of photos in the photo thread.