I'm still getting a rally bad stumble from idle on my '69 pontiac 400 with an 800 D/P carb. I know that everyone will say that carb is too big but it ran absolutely fine last year. Ive upped the accelerator pump nozzle in the primary from a 31 to a 40 but still exactly the same. When I first fitted this carb last year it was to try to see if I could get into the 13's from a regular 14.2. It immediately done a 13.8 so obviously didn't have a problem then. Any suggestions please?