Bad running

[Hobbo]

Hi all, help needed with poor running, car starts o.k. but when acceleration is applied it pops/ backfires in exhaust, this is at standing position have not yet tried out on road. Have checked points, plug gaps all o.k. previous owner had set timing, have tried mixture control on carburettor but it makes no difference, plugs were very sooty  which points to I think over richness.  Any ideas, Thanks Mike.