Hi chaps,
There is undoubtedly a very simple answer from the more knowledgeable amongst you, but here's the question:
As some here will know, I recently spent several arms and legs on a Norman SC - and very nice it is too!
When I received it, it obviously had not been run for a long time and needed all manner of cleaning and tweaking to get it running.
One thing I thought odd was that initially it was kicking back a lot. I had decided that the stupid cranking handle was going to do me an injury before the thing ran so I attached my high torque drill to the flywheel nut to give it a good spin. The thing was kicking back so hard that on the odd occasion when it actually fired it stopped the drill dead (or rather it tried to turn my arms into something resembling a twisted rope). The obvious thing, I thought, was ignition timing. I checked and found that it was spot on. I decided that, in the interests of science and a broken forearm, I would retard the ignition to the point where it would fire just after TDC, after all, the thing couldn't possibly kick back in this condition - could it? It bl***dy well did! In fact it made no difference.
Anyway, after working my way through all the normal things (points, ignition timing, valve timing, valve clearances, fuel supply, carb. jets etc, etc), it now runs superbly and I've now returned the timing to the correct setting (it's still a bu***r to start using the wholly inadequate cranking device though)
So, the question: how can an engine, retarded to the point where it is firing after TDC kick back? I guess that when its cranking over and not firing properly there's all sorts of undesirable conditions going on in the fuel department but that doesn't seem to account for the kick back.