Hello, I bought an El 252 year 1997 for my wife who was not with the TÜV for two years. Test run and driving test (small private area) was fine, the only error was the switch from the side stand which was not operated. After the change of the switch works again, I started the engine about 10x. One day later I wanted to start again but the engine knocks and does not jump properly. I drive myself an LTD 450 d he had the same problem 2 years ago. CDI renewed, ran again to 100%. In the EL 252 I installed the CDI of an EL 250B, which according to the dealer is identical. Unfortunately the knocking is still there and it does not start at all. Oil and oil filter I had immediately renewed 2years ago the El was overhauled at the dealer for 960€ and prepared for the TÜV but not presented (illness of the previous owner). What can I do yet, what did I do wrong, fits the ignition unit of the EL 250 I’d be happy for tips and hints.