Author Topic: Post 75' Q-jet jet/rod sugestions  (Read 2911 times)

Offline 351wpower

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Post 75' Q-jet jet/rod sugestions
« on: November 25, 2014, 08:40:05 AM »
Any members have luck jetting a post 75' with big air bleeds. Looking for a jet/rod combo that would mimic a jet/rod combo for an earlier pre 75'
                                               (WITHOUT CHANGING AIR BLEEDS)

Question: If you were running a pre 75' with small air bleeds and found a recipe that worked well,
Say 71-73 jet, 44 primary rod and a CC secondary rod.

Now if wanting to keep with those specs, But using a post 75' with the larger air bleeds. Is there a formula or a rule of thumb that I can use to pick a jet/rod combo.

I'm not looking for a combo based on the (year, make, model, engine, gears. (This info is everywhere)
I'm looking for some sort of conversion or.

If 2 Q-jets were on the bench:             1st. pre 75' small air bleeds     72 jet, 44 pri rod, CC sec rod
                                                         2nd. post 75' large air bleeds   ________________________             

Offline 351wpower

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Re: Post 75' Q-jet jet/rod sugestions
« Reply #1 on: December 02, 2014, 09:43:40 AM »
So its safe to say if you don't identify yourself as someone who has bought the (BOOK) then you only get vague borderline insulting answers like (lean, rich, probably to much/little .............)


Little to no suggesting's for jet/rod combo's here, but lots and lots of basic specs and nomenclature which can be found much easer and faster elsewhere. 

This site is the poster child for answering a question without really answering the question   



 

Offline Ethan1

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Re: Post 75' Q-jet jet/rod sugestions
« Reply #2 on: December 02, 2014, 04:56:04 PM »
 Patience....
Ethan

1972 Chevelle

(oo______oo)

Offline Cliff Ruggles

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Re: Post 75' Q-jet jet/rod sugestions
« Reply #3 on: December 18, 2014, 06:23:11 AM »
I have excellent results with the post 1975 LMAB models all the time.

Even so, there is no "specific" answer to your question, we don't deal with "rule of thumb" or calculations based on jet/rod metering area when setting up carburetors.  Although all that stuff looks good on paper, it's next to useless in practical application as airbleeds have as much as or more effect on fuel delivery across the load/speed range and changing out jets and metering rods.

In any and all cases, these carburetors need to be set up or calibrated EXACTLY for the application. This is done based on carburetor number, how that carb is set up from the factory, and all of the engine/drivetrain/vehicle specs.  Correct fuel delivery starts with the idle system, as it feeds the main system thru transition, so each calibration we suggest or use is actually application specific.

There is no direct correlation between a post 1975 carb for any manufacturer and an pre-1975 carburetor.  There just too many applications, different types of carburetors and different calibrations.  Chevy carburetors from 1970 thru 1976 divorced or hot air choke will be large MAB. After 1976 the divorced choke truck carbs were SMAB, and they introduced SMAB into the hot/air electric units in 1979, but some models were still large MAB to 1980.

Automotive carbs post 1980 will be computer controlled, as were CA emission truck carbs post 1981.  48 State truck carbs were non CCC till 1987 when they switch to TB's......Cliff