Tuning our Shelby’s Carburetor

To change the jets, you must remove the carburetor; fortunately, it only takes about 10 minutes.
The Holley jets themselves are quite small. To properly tune a car, you will need a decent jet selection. Fortunately, old-style Holley jets fit the new HP carbs.
Adjusting the Crane ignition curve is easy if you use the tool that comes with the kit. There are many settings to choose from that change total advance as well as advance curve.

An air-fuel ratio of over 14:1 is certainly not where you want to be for safe driving and maximum efficiency.

With the Texas 1000 rally behind us and the Shelby GT 350’s problems sorted, it was time for a bit more tuning and some corner weighting.

Our initial dyno testing revealed that the engine was running too lean. An air-fuel ratio of over 14:1 is certainly not where you want to be for safe driving and maximum efficiency. We moved from No. 76 jets at all four corners of our carburetor to No. 80 jets on the primaries (front of the carburetor) and No. 81 jets at rear (secondaries) of our carb. This setup turned out to be too rich, so we moved back to No. 78 jets at all four corners.

We then fine-tuned from there by adjusting the idle circuit mixture screws. When driving at highway speeds, a car is still partially using the idle circuit; it’s only turning a couple of thousand rpm.

The Crane ignition system we chose has several preprogrammed settings. These settings combine total timing with how quickly the advance comes in to meet different needs on various engine configurations.

We chose setting No. 7, which was for a high-powered, fairly light car with an aggressive cam. Once we got to the dyno again, we tried different settings. However, this initial choice proved to make the most power and gave the car excellent drivability.

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