Proud Cobra Owner - SP01862

[wkooiman]

If the Holley Street Avenger was brand new, it should have worked fine right out of the box. There are differences between each carburetor model, of course, but they are not so great to cause the engine to run like crap. You likely have a different problem.

And if you really made 470HP with a 750CFM, and you switched to a more radical camshaft, you are going the wrong way by using a 650CFM carburetor.

You need local help from someone that knows what he is doing. Carburetor tuning isn't difficult, but it is a dying art.

My favorite carburetors are from Quick Fuel Technology. They build excellent carburetors based on Holleys. Another good choice is the Holley HP series. I'm suggesting this over the others because you said you have a more radical camshaft. They carburetor and camshaft need to work together.

My favorite carburetor tuning website is this: Carburetor Tuning the Scientific Way

There is a section near the bottom where he explains how to tune using an O2 sensor and a vacuum gauge. I did this on my car (non Cobra), and it made tuning a piece of cake. The O2 sensor eliminates the guesswork.