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tuning rochester

2222 Views 6 Replies 6 Participants Last post by  1982 SS
how do i adjust fuel mixture
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Welcome aboard.
It would be helpful to have some more info like engine, hp,setup, carb model.
Basic, If you are adjusting the idle mix, the two screws located at the lower front of the carb. In for lean, out for rich. Off idle mix is adjusted by changing jets and needles. From your post, I gather you are new at this so, go to you local performance parts house and buy a tech book on whatever carb you are working on. :)
study study study those tech books! :thumbup:

especially if they have both basic info for people new into the hobby as well as advaced tuning tips.

The Qjet is a good carb, they just take time and patience to tune, more involved than a simple Holley. :thumbup:
Yeah the Qjet is a great carb when done correctly. Unfortunately, many a person does not take the critical time required to make the correct adjustments. It is just a matter of time. Your fuel delivery system is controlled by a couple main factors. The size of the jet hole and the actual size of the metering rods, which includes the tapper of the fuel rod and size of the diameter. This is all done in pairs. You have two low speed jets, two high speed jets, and two rods. And all three of these will effect the other if done incorrectly. Plus your altitude will play a significant roll in the matter as well. You are at sea level, which constitutes altitudes up to 2500' in elevation, and then you are in the mountainous regions, which cover altitudes up and over 3000' above sea level. The air is thinner and less dense with moisture. Hence your engine reacts differently in altitudes.

Get a book, a Haynes manual or Chilton's will do from the parts house, and read till you can recite the book and have a mentor around to help explain the little stuff to you. Good Luck and take your time.
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I highly recommend a new book by Cliff Ruggles that came out this summer on the QJet. Do a search by author on and you will find it. About $25 at Borders Bookstore.

I have been twiddling with my QJet for over a year and it all came together when I got this book.

I've been thinking, of getting a Rochester for the Javelin (amc 360). Right now it's got an old school Holley 4bbl on it, and wonder if swapping the Rochester would be a bolt on thing, I'm looking for more precise mixture control (my logic says it would help driveability, spark plug life, and mpg, if you have experience let me know).
I don't know if the AMC's have provisions for a spreadbore... I would be cool if it is, cuz I really like my Q-jet. Each time I go through one, I get better about finding out the little things that make all the difference, and how not to blow carb cleaner in my face with compressed air. For example my first rebuild was a very slow process that did not even involve the idle circuits. I did not figure out exectly how the idle circuits worked until I took the Q-jet of my race motor (weird unexplainable surging problem at WOT, that went away after I cleaned everything and epoxied the plugs). I had problems with a previous build that got sidelined (mom's car and the gutless 267 was deemed to not have enough power to be "safe"), but I now have enough knowledge to make it work after the 350 goes in to replace that little 267.

Remeber the mantra:
Knowledge is Power. In this game, it really is. The little things make the most difference.
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