Is the valve spring length in the C12 instruction manual correct, they are written as free length for outer 2 inches and inner 1-17/32 inch. I bought some new ones which turned out to be same length as my original ones removed, outer 1_7/8 inches and inner 1-7/16 inches.
I had the same thing with my C11G. It turned out that the new springs were made of a different thickness of wire and gave more resistance for the same amount of compression. I fitted them and they are absolutely fine. Cheers, Roland.
Thanks for the info
Simon