I haven't run my car since last September until today, when I parked it up all was working well. All I've changed is the carb over the winter. When I took it for a drive today, in Drive it was changing up fine, but when it got below 25mph it changed down gear rather quickly, to the point where it was really jerky, and it never did before it was parked up, it changed down smoothly. Any ideas why it would be doing it now? It's a c4 behind a 302.