Hey all, Finally got all of the little thing together on my project Z28. Now that shes running, shes running rich. I have a 79 350 bored .030 with the stock heads mildly ported with a stock Iron spreadbore manifold. (switching to vortecs this spring) On top I have an Edelbrock 1901 Qjet with an electric divorced choke. I adjusted the choke to run more lean which helped greatly. Now I just have to adjust the mixture screws. My question is this. The instructions call for me to adjust one screw for max rpm or vaccum, then set idle speed then set other screw for same and so on and so forth. Has anyone adjusted one of these before? If so any pointers? The tech data from Edelbrock is very vague. Thanks in advance.

Bill

 

When I setup my Edelbrock Q-jet I first set the idle speed screw to the idle rpm I wanted. If it won't stay running where you want it speed it up to where it stays running. Then I hooked a vacuum gauge to the vacuum port at the base of the front of the carb. I then adjusted the mixture screws to get the most vacuum and then readjusted the idle speed down and readjusted the mixture screws for max vacuum and then gave them and extra half turn out. As soon as the vaccum stop going up is when I gave the extra half turn. After you set one mixture screw set the other and recheck the one you did first. My Q-jet idles good once its warmed up. I have yet to hook up my electric choke. I have the choke zip tied open for now.

Hope that helps.

 

Idle mixture screws should be adjusted EVENLY side-to-side. Set them 4 turns out from LIGHTLY seated for starters and set your idle speed so it's ROUGHLY right. Then start turning the idle mixture screws in 1/2 turn at a time- EVENLY SIDE TO SIDE. Keep going until the idle obviously slows down just a little (and it will sound "rough" or "flat" to the ear). Back the idle mixture screws out EACH 1/2 turn from there. Readjust your idle speed until it's back where you want it. Go another round on the idle mixture screws in the same fashion as before. You should now have it roughtly right. You may want to go through this whole prociss another round or two to make sure it's dead-nuts perfect. Sometimes one mixture screw will want to be SLIGHTLY further in or out than the other just due to production tolerances inside the carb but generally they'll never want to be set more than about 1/2 turn different from eachother. But that's for the last round of "final tuning." Up to that point always adjust them exactly the same.

ALWAYS DO THIS PROCEDURE ON A FULLY WARMED UP ENGINE. If you set things when it's still a little cold it will be slightly "off" once the engine is fully warmed up.

You'll get the hang of it pretty quick once you've done it correctly the first time or two. Your "feel" for this will grow quickly. Once you do it right, you'll know. You'll get an intuative "feel" for this procedure real quickly.

 

Thanks for the replies. I will try both methods and see where I get. Quick question though, When the carb is running rich how much black smoke willl come out the exhaust? Mine was nauseating at first but then I set the choke correctly so now it just kind of noticeable. Thanks again!!

Bill