Thanks for the response, we haven’t checked the timing accurately, we’ve only checked that the spark was happening with the piston “near” TDC to ensure the HT leads were the correct way round, it is “trying” to run like this. We only tried swapping the leads as a last resort as we’d tried everything else ! and it felt as though it was trying “not to run” like that so swapped them back. I would have expected it to start, even if running irregularly with the timing not spot on?
No we didn’t strip the whole engine, just the barrels and crankcase doors, and yes it is a distributer, which we didn’t “move” when stripping the engine.