General Category > Quadrajet Carb Talk and Tips

q-jet idle

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prostreet64:
Cliff, that is exactly what we are looking to accomplish by going to a q-jet. It might be possible to achieve a 'good' idle with the current Demon carb. but we want to give the q-jet a try, and besides I always like to see the look on peoples faces when you pop the hood and they see you are running a quadrajet instead of a Holley or equivalent. Our cam in the Bird is on the 'big' side for a 400 motor; 248/254 @.050 but even so I am sure we can improve idle quality with the right carb and timing setup.

Cliff Ruggles:
That is a big cam for a 400, hopefully it's a high compression engine?  Still no problem getting it to idle well.

The q-jet has an excellent idle bypass air system which really helps idle quality with big cams. It diverts idle air around the throttle plates and comes in under them.  This is a controlled vacuum leak, and big cammed engines need this to help keep the throttle plates low enough to stay on the idle system instead of pulling fuel from the main system.....Cliff

prostreet64:
Cliff, the c.r. is right at 9.7. Over the years as we have looked for more horsepower, our goal has always been to maintain a pump gas friendly combo, so with the iron heads we are keeping the c.r. in a safe range. I was talking to my son last night and we are pretty excited about getting a q-jet and rebuilding it per your recommendations and specs. As soon as we have a core I will be ordering the parts that we need.
Gates

prostreet64:
Cliff, my son was talking to a friend of his that has a repair shop and after he learned that we planned to replace the Demon with a q-jet he gave us 4 units that he said had been sitting around for a long time. They all appear to be Chevy applications; one 1971, one 1972, one 1980, and one 1984. Here are the #s, do you think one is a good candidate for our buildup? 7042208, 7041209, 17080204, 17084226. If one of these is a suitable core then I am ready to get the parts on order. Thanks,
Gates

Cliff Ruggles:
I'd use one of the later ones, preferable the one that is in the best shape and most complete....Cliff

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