I realize this topic may have a very limited interest but it was a good Avanti day and I thought I would share what I've learned. Some of you may recall that I mated the top of an R2 AFB to a 600 Edelbrock. Over the past few years I've never been happy with the overall performance of the car. I have 3 other cars, non-Studes, that have E Carbs on them and with each one I've been able to tune the carbs to a point that the responsiveness and acceleration rivaled my fuel injected modern iron. The Avanti never "felt" right and had a sever power drop and mis-fire at about 4500 rpm. Even before it reached this critical point it just didn't pull as smoothly as my other carbed cars.
Last summer after months of experimenting with jetting and timing, I decided to devise a way to hold the air valve in the secondaries open. I may not be calling it by it's proper name but it's the flap above the secondary throttle plates that keeps the car from bogging when the secondaries are snapped open. It allows the engine to determine how much air it needs by opening as the vacuum below becomes greater than the air pressure above. To my surprise the high speed miss went away and the car accelerated better. I drove it that way all summer but on a couple of drives in the cooler weather the lack of a functioning valve was very apparent, compounded by having blocked the exhaust crossover, the car bogged terribly even at less than full throttle.
A couple of weeks ago I took the bottom half of my old AFB and did a visual comparison between it and an Edelbrock 600 parts carb I have. First thing I noticed was that the air valve on the AFB lays flat and closes the secondary holes completely while the E carb's valve is already partially open. Makes sense for a HP carb to get the air moving faster but I wondered if the partial opening allowed compressed air to build up under the valve and keep it from opening or making it flutter. So I ground enough off the valves weights to allow it to close fully.
I also noticed that the primary venturi clusters on the E carb had a shorter air bleed tube that didn't reach up into the AFB top. I changed out the E venturis and put the old AFB units in. While I had the top off I put in a larger .110 needle and seat and # 33 as opposed to #31 pump nozzles. The AFB appeared to have larger ones than the E carb. I jetted down the primaries from the .101 that I was running and went back to the .98 and
75/47 rods that the E carb comes with as standard jetting. I switched the .101's to the secondaries so I have the same amount of fuel as I had before under full throttle but a leaner cruise and part throttle A/F considering the state of gas prices.Initial results are very encouraging. There was a slight drizzle this morning when I was doing my test driving so I didn't go crazy but the car pulled cleanly to 5000 rpm, no miss no flattening. The real success is in the throttle response and the nice smooth pull throughout the rpm range. I think the AFB Venturis are responsible for this.
I almost gave up on the AFB/Edelbrock hybrid and went with a different carb hat to match the blower to the Edelbrock but I liked the stealthy look of the Hybrid too much to give up without one more experiment. Glad I did.
Ernie R2 R5388