Whats the difference Stage one Qjet vs 455 Qjet

Discussion in 'The Venerable Q-Jet' started by Oldskewl59, Jul 11, 2012.

  1. Oldskewl59

    Oldskewl59 Gold Level Contributor

    So I decided to check the carb id. Its 7041242 with a date of 2576. So that is a 1971 stage one Qjet service replacement made in 1976? I don't have a stage one car..so what is the difference between that and the one I should have ( which is 7041540)? Just the size of the jets? Car was built Sept 1970 in Flint.
     
  2. vonwolf

    vonwolf Silver Level contributor

    I see the date code looks like it says 257th day of 76 but the carb number 7041242 says its a 71, I think it is off a 71 as for the difference from a non-stage carb I'm not real sure other than bigger jets and metering rods. It would be a nice carb to have thats for sure
     
  3. Oldskewl59

    Oldskewl59 Gold Level Contributor

    I thought 2576 was the 25th of July,1976, but I may be wrong.
     
  4. vonwolf

    vonwolf Silver Level contributor

    That is confusing because thats the way I see it also but the carburetor # is what I'd go by 7041242 is a carb from 1971 "7041" if it was from 76 it would be "17056" so its kind of conflicting and I would go with the 7041 making it a 71. I might be reading it wrong but at least it is a stage 1 carb and that what's really important

    Unless its a replacement carburetor for a 1971 made in 1976? I guess thats possible.
     
  5. Marco

    Marco Well-Known Member

    Pete is correct.

    4 digit date code starts with 3-digit Julian date and last digit is year of manufacture. If year of manufacture > year of carb part #, it's a replacement carb.

    Difference between stage1/non-stage1 is jets/metering rods
     
  6. Oldskewl59

    Oldskewl59 Gold Level Contributor

    Thanks. Just wasn't what I expected to see and I wanted to make sure what I had.
     
  7. robs71redriv

    robs71redriv robs71redriv

    heres 71 4mv carb spec page from the 71 chassis manual
    4mv specs  1971 Buick All series Chassis SM.jpg 71-73 manuals and more on carbs can found in the Boattail Registry Library - including a handy refferece of extracted charts with the above specs and adjustments for 71-73
    http://boattail-riviera-by-buick.com/library/documents/71_73%20qjet%20specs%20adjustments/index.html

    and how to make the all the adjustments internal and external plus trouble shoot clean and inspect etc

    http://boattail-riviera-by-buick.com/library/documents/1971%20qjet%20clean%20adjust/index.html
     

    Attached Files:

  8. Oldskewl59

    Oldskewl59 Gold Level Contributor

    Thanks Rob! That settles that.
     
  9. Jim Jones

    Jim Jones Wretched Excess

    I do not have a '71 Stage 1 carb to verify, but in 1970 there was also a difference in the location of the outlets of the secondary enrichment circuit. On Stage 1 carbs (7040246), these exited below the secondary air valves. The 7040240 carbs had outlets located above the valves. You may want to check the outlet location on your 7041242 carb. All of the 7041540 carbs I have in my possession have outlets above the valves.
     
  10. techg8

    techg8 The BS GS

    this is correct (below the airflaps) for every stage 1 qjet I have seen, and a great way to tell if its a "real" stage 1 air horn.
     
  11. wildcat4

    wildcat4 Well-Known Member

    Great info guys!
    I wanted to respond so I could find this thread in the future.
     
  12. HotRodRivi

    HotRodRivi Tomahawks sighted overseas

    The 4mv 1976 off any buick is the best carb and eaisiest one to find at the wrecking yard these days. They have the big main body factory 800 cfm. and slashed bowl vent in the front. That and just about any one u find on a pontiac are the only ones worth using in my opoinion. Grab urself a rochester book and go to town.
     

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