fia#09,
He's half right (your local machine shop guy), double pumpers do have the potential to cause more of a cylinder wall wash-down effect than vacuum secondary carbs, but it has nothing to do with bumpy roads. I doubt the roads in Endwell, NY are that bad or you'd be driving a 4x4 instead of a Cobra!! It depends on a number of factors such as how well or how poorly it's been set-up and how active your right foot is.
Actually, a vacuum secondary carb is just as potentially damaging if it hasn't been set-up correctly and is running too rich.
Initially, I installed an 850 DP (big block spread bore 4165) carb on my engine and it was dumping in way too much fuel. My engine was dyno'd with a 750 DP so I didn't think an 850 was too out of the question. I was wrong, so I switched over to a 600 cfm vacuum secondary that I had laying around and other than the fact that it has a very slight off idle lag, it performs flawlessly all the way up to redline (my engine really roars to life when I drop the hammer!!!). I switched to the 600 as a temporary measure with the intent of putting on a 650 DP eventually, but truthfully, for a mostly street driven car it isn't necessary and my car runs great with the 600. The only changes I made to it were to change the vacuum spring to the lightest one available and I installed a new pump diaphragm and an agressive pump cam.
Interestingly, I have a complete Weber IDF system that I'm planning to install, but the car is running so well as it is, I'm hesitant to mess with it right now.....
Mike
