Set-Up Procedure

For those people who don't know where to start when they first install their carburetor, let me offer you the procedure I use. Please also to refer to page 32 of FM's AFB procedure while you are doing this. While this procedure was used to set up a carburetor on an inline engines, it should also be reasonably applicable to V-8s. Before you do any work, I would recommend that you track down Carter Carburetors by Dave Emanuel and study it well. Before you start, make a note of what metering rods and jets are in your carb.

If you have any intention to install headers, do it before you start setting up your carburetor because the availability of intake heat will affect the set up. I recommend that you keep the exhaust manifolds for street engines because you can retain the heat riser system. Personally, I think engines look so much cleaner with manifolds anyway. Without the heat provided to the hot spot in the intake manifold below the carb, the fuel mixture will have a tendency to lean out on acceleration because the fuel tends to fall out of the air to puddle on the floor of the intake. Having said that, if your V-8 intake manifold doesn't have an exhaust cross-over passage, you may want to consider removing the heat riser valve to slightly improve exhaust flow. Do not remove the manifold heat control valve on inline engines.

Before you do any metering rod and jetting changes, and assuming your carburetor is in good working order, install everything and see how well it runs. Once you have a baseline fuel economy and even a few runs down the drag strip, you will have some idea whether any changes are really improvements. Start by trying to tune the main metering system first. You could do this by either tackling the cruise mode or the power mode of the carb. If this is a daily driver for you, you might want to the cruise mode first. Otherwise, try setting up the power mode first. Start off with the weakest metering rod springs and the smallest accelerator pump shot.

For the cruise mode, the quickest and most reliable way of determining the best rod and jet combination is to drive at steady highway speeds long enough to get a repeatable gas mileage reading. Keep leaning it out until you get the best gas mileage or until you find the car has a lean surge. Your best gas mileage will likely be with the combination that is just richer than what causes a lean surge.

Remember, lean fuel mixtures burn slower. At some point, should also consider increasing your vacuum advance (with an adjustable vacuum advance) in 1-turn increments until you find the point where your fuel economy starts to drop off or begin to notice audible knock (or pinging). Then decrease your vacuum advance 1/4 turn at a time until the knock disappears or your gas mileage peaks.

The power mode is a bit trickier because too much acceleration will cause the secondary metering system to kick in. I would disconnect the secondary linkage so that your carb functions as a 2bbl. Be careful not to lose the clips. When accelerating, too lean a setting will cause an off-idle bog when the fuel falls out the air stream as manifold vacuum drops. A somewhat scientific way of setting this up is to find a straight, lightly traveled section of road and measure your 0-60 (or 0-70, etc) mph time. The metering rod & jet combination that gives you the quickest time is your power step setting. Be careful as too high a terminal velocity may cause you problems with the local constabulary.

Once you have determined the best cruise and power settings, you need to put them together on the same metering rod & jet if you already haven’t done so. Calculate the flow areas for each case and find the combination that comes closest to them. It’s OK to go a little richer on the power step if it makes your selection easier. Drive your car and try out gradually stiffer metering rod springs. Pick the one that makes the car feel most responsive. Remember, the stiffer the spring, the more fuel your car will consume. If your car has a stumble on acceleration, gradually increase the pump shot.

Once you've set the main metering system’s jets and rods, reconnect the secondaries and go back to that section of road you were using before. Adjust the secondary jets until you have the best time. Make sure you do your testing when traffic is minimal.

I hope you find this helpful. You might find a better procedure for setting up your carb but I think what I’ve suggested is probably a good starting point. If you do find a better procedure, please let me know!