Hi Dave - thanks for your post - I have made sure the cog lines up each time but that is a very good point
Daniel - I remembered your post from a while back and checked it before my post - I have pretty much done everything you recommended, and had a bit more cleaning to do as the coil plugers were covered in soot
It seems I need to replace the springs - can you just buy these at a hardware store? Am I looking for the length of the spring or number of turns?