Originally Posted by hpete
It's 600 cfm at 1.5 inches of mercury which is nearly 20 inches of water. Pretty restrictive if you think about it. It means that in order to pull 600 cfm through it your vacuum guage would have to be on 20. What really gets me about these small carb fans is that they don't understand who controls the opening rate of the throttle blades.
there isn't a single carb out there that flows what it is rated at, most are under, a few are over.
And as for what controls the throttle blades, on a vacuum secondary carb its the spring, which can be easily swapped out- if it needs to be.
A quick test is with your pedal to the floor what is your vacuum gauge reading? You can lower that number (to a point) by adjusting your vacuum secondary spring. A 600 carb will be more than enough for most 350's up to about 5,000 RPM (with a proper spring of course) most people never rev that high, if you don't then a 600 would be fine BUT that's not to say it would be better than a 750. A 750 carb can also work very well but again may just need some spring adjustment.
That is of course assuming your fuel metering is spot on- which it may or may not be.