I recently bought this carb to replace a Carter 600 cfm. The main reason I switched is because I was looking to get more low end torque. But I was also hoping with the annular discharge nozzles that fuel would be atomized better, resulting in cleaner exhaust. My car has never been able to pass the emissions exhaust test we have.
My motor is a 306 with XE262H camshaft, headers, and RPM Airgap intake. This is mated to a T5 transmission and 3.00 open rear gears (for now).
I've had driven the car for only one day but the difference is unmistakable. Low end torque / throttle response is definitely better. With the Carter, if I was rolling in 1st gear and punched the throttle, the tires would not break loose. Now they will break loose. Also, the car pulls hard to 5500-6000 rpm. So I really don't think I've lost anything at higher rpms.
I don't know yet if I will be able to get through the emissions exhaust test as-is. I adjusted the idle mixture to try clean it up the exhaust as much as possible. The exhaust still has the odor of a car with no catalytic converters, but it doesn't seem as bad. I did notice that I now get about 17" vacuum at idle. I never got better than 15" with the Carter. So I assume that means the engine is burning fuel more efficiently, at idle anyways.
The carb needed minimal adjustment out of the box, mainly just the primary float being too high. Cold idle RPM is about 1200 rpm on my motor, which seems to be fine. The choke comes off after only a minute or two. With my Airgap intake though, choke needs to stay on for a few minutes longer or the engine stalls. So I will see how much I can adjust this.
So far I'm very happy with this carburetor.