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There's a lot to be said for simplicity, and a great example is a carburetor compared to fuel injection. It goes without saying that electronic fuel injection is sophisticated and can be easily tuned to maximize mileage and performance, however those features come at a price—not only financially but in complication as well. Granted, carburetors are old school and low tech when compared to EFI, but they are simple, effective, affordable, and are easily tuned.
Recently, we did some trading and came home with a low-mile, rebuilt Chevrolet engine. Compression and leakdown testing indicated that the engine was in great shape so we decided to add a cam, headers, electronic ignition and drop the small-block into one of our project trucks.
Along with its excellent condition we were fortunate that the engine was equipped with an Edelbrock intake manifold and cfm Edelbrock carburetor. While the engine tested well, when we fired it on a test stand there seemed to be some carburetor issues, the accelerator pump wasn't working and the idle was erratic, symptoms that indicated a freshening up was in order—in most cases that simply means a thorough cleaning, a new accelerator pump, needles, seats, and gaskets.
With the carburetor disassembled the first thing that caught our eye was the amount of varnish and debris in the float bowls. It was obvious from its condition this carburetor had been sitting for some time. Given its internal signs we were sure the air bleeds would be plugged, something that was confirmed with some small-diameter safety wire this needs to be done carefully so critical calibrations aren't destroyed.
Given the condition of our carburetor it was obvious it needed to spend the night in carburetor cleaner. Once out of the solution it was simply a matter of reassembly, but there was another issue that we had to address—jetting. Normally that's something that is best done on a running driving car, but in our case someone had installed extremely large primary jets so we elected to return to the original baseline settings.
For our model that required 0. Edelbrock carburetors have the following systems that can be adjusted:. At idle percent fuel is delivered by this system. It also meters fuel at off-idle throttle positions—a large percentage at just off of idle decreasing to a minor amount as the throttle is opened wider.
The idle setting is critical both to a smooth idle at proper rpm and to a smooth transition to part-throttle operation. The Edelbrock main system has two modes—light load cruise and heavy load power. Under light loads manifold vacuum is high and the step-up pistons are pulled down, moving the large diameter of the metering rods into the jets producing a lean mixture.
When the engine is under a heavier load the step-up springs overcome the pull of vacuum on the pistons, they move up and the smaller diameter of the metering rods in the jets provides a richer mixture. Another adjustment is the staging function or when the metering rods change from one mode to the other. The movement of the metering rods is controlled by the step-up springs—the base calibration has springs that "stage rich" at 5 inches Hg.
According to Edelbrock's tuning guidelines, in cases when there is a mid-throttle driveability problem as the throttle is gradually opened but then goes away upon further opening, it may be possible to eliminate the lean spot by using stronger step-up springs from the calibration kit.
Edelbrock also advises it's best to select a new spring on the basis of vacuum readings, but in the absence of a gauge, try the strongest spring highest vacuum rating to see if the problem goes away. If the drive problem is cured by the strong spring, try the next weakest spring as well.
Use the reference chart in the calibration kit to help select another combination. The secondary system delivers fuel only when the secondary throttle blades and air valve are open, which takes place when the primaries are about 65 percent open. The primary and secondary throttles reach wide open at the same time.
Calibrating the secondary system is done by changing jets. The best way to determine jetting needs is with a chassis dyno or by making timed acceleration runs, however, we've never found it necessary to change secondary jetting from baseline for a street engine. The accelerator pump has an external pump lever with three holes that result in three fuel delivery curves.
Moving the rod closer to the carb body increases the accelerator pump "squirt," however, if the idle and primary calibrations are correct the base adjustment middle hole should be sufficient. The electric choke is adjusted by rotating the cover clockwise against the internal spring. The suggest setting is two notches rich past the long center index mark. At idle, fuel pressure should be no more that 6 psi. If fuel pressure exceeds 6 psi Edelbrock recommends a regulator, such as PN In addition, a filter, like Edelbrock PN , should be placed between the pump and carburetor.
Our Edelbrock carburetor was in good shape, the throttle shafts were tight so vacuum leaks were not a concern, the gasket surfaces were flat, and the body and airhorn assembly were in good condition with no stripped holes. The only real issues were deposits from old fuel and the wacky jetting change and those issues were cleared up with reasonably priced rebuild and recalibration kits. Cleaned, rejetted, and regasketed our Edelbrock carburetor is ready once more to mix fuel reliably for many miles to come.
Ron Ceridono Author. Borderline for part throttle driveability worse than borderline if EGR is used. Share on Facebook Share on Twitter.
Very Rich: Some supercharged engines run in this range at full power as a means of controlling detonation. At
Edelbrock Performer 1406 Manuals
It runs pretty well. This is a popular carb for the small block Ford and is the trickiest Performer carb to tune. Edelbrock parts are a bolt on deal, no massaging parts or gaskets to line up properly. The gasket may be covered underneath by the edges of the manifold and above by the carb, but there are places the gasket doesn't get "sandwiched" between the two to create an air-tight seal. From what im reading here sounds like would maybe better choice if not worried about growing with it. What's the best electric fuel pump for the edelbrock carb? I've read some threads that say edelbrock carbs are finicky on fuel pressure, but I don't want to have to buy a fuel regulator if I don't have to.
Rebuilding And Tuning An Edelbrock Carburetor