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Jets and Metering Rods

 

Carburetor Jets and Metering Rods

Here is a list of the carb #'s, along with the #'s for the jets, primary rods and secondary rods. These are the #'s from the AC-Delco manual, so they are only as accurate as that is. Also beware that I am just copying what is in the book(s); thus any errors or inaccuracies there are here as well.

Especially interesting are the 1970 W-30 and W-31 with manual transmissions; it looks like those Quadrajets used the 2-bbl jets with no metering rods! (this has been confirmed by some original W-30 owners; note this is only the 1970 M.T. applications)

Year & Application   Carb #   Main Jet Primary Rod   Secondary Rod
1966-
400/425 M.T.         7026250  7031971  7031844- "44" 7033655- "AU"
330 M.T.             7026254  7031971  7031844- "44" 7033658- "AT"
400 A.T. w/o A.I.R.  7026256  7031971  7031844- "44" 7033655- "AU"
330 A.T. w/o A.I.R.  7026255  7031971  7031844- "44" 7033658- "AT"

1967-
330                   7027036  7031971  7031844- "44" 7033658- "AT"
330 w/ C.C.C.         7027135  7031971  7031845- "45" 7033658- "AT"
330 w/ A.I.R.         7027153  7031971  7031845- "45" 7033658- "AT"
400/425 w/o A.I.R.    7027156  7031971  7031844- "44" 7033655- "AU"
400/425 w/ A.I.R.     7027157  7031971  7031845- "45" 7033655- "AU"
400/425 w/ C.C.C.     7027032  7031971  7031845- "45" 7033655- "AU"
400 M.T. w/O.A.I.(5)  7027156  7031971  7031841- "41" 7033655- "AU"
425 Toro w/o A.I.R.   7027131  7031971  7031844- "44" 7033655- "AU"
425 Toro w/ A.I.R.    7027130  7031971  7031845- "45" 7033655- "AU"
425 Toro w/ C.C.C.    7027132  7031971  7031845- "45" 7033655- "AU"

1968-
350                   7028250  7031971  7034849- "49B" 7033658- "AT"
350 w/ W-31           7028255  7031974  7034849- "49B" 7033658- "AT"
400/455               7028251  7031971  7034849- "49B" 7033655- "AU"
455 Toro              7028252  7031971  7034849- "49B" 7033655- "AU"
400 W-30              7028254  7031975  7034849- "49B" 7033655- "AU"
400 442             7028253  7031972  7034849- "49B" 7033655- "AU"

1969-
350                   7029250  7031970  7034849- "49B" 7033658- "AT"
400/455               7029251  7031970  7034849- "49B" 7033655- "AU"
455 Toro              7029252  7031970  7034849- "49B" 7033655- "AU"
400 M.T.              7029253  7031972  7034849- "49B" 7033655- "AU"
400 W-30              7029254  7031975  7034849- "49B" 7033655- "AU"
350 W-31              7029255  7031974  7034849- "49B" 7033655- "AU"

1970-
350                   7040250  7031970  7040701- "52C" 7033658- "AT"
455                   7040251  7031970  7034849- "49B" 7033655- "AU"
455 Toro              7040252  7031970  7040701- "52C" 7033655- "AU"
350 W-31 (6)          7040255  7002657     -           7033655- "AU"
455 442 MT          7040253  7031969  7040699- "48C" 7033655- AU"
455 W-30 M.T. (6)     7040256  7002658     -           7033655- "AU"
455 W-30 A.T.         7040258  7031969  7040701- "52C" 7033655- "AU"
455 W-33, 442 A.T.    7040257  7031969  7040701- "52C" 7033655- "AU"

1971-
350                   7041250  7031970  7034849- "49B" 7038256- "AS"
455                   7041251  7031970  7034849- "49B" 7033104- "AK"
455 Toro              7041252  7031970  7034851- "51B" 7033549- "AX"
455 M.T.              7041253  7031969  7034849- "49B" 7033655- "AU"
455 A.T.              7041257  7031969  7034849- "49B" 7033658- "AT"

1972-
350                   7042250  7031969  7034850- "50B" 7045778- "CG"
455                   7042251  7031969  7034850- "50B" 7045779- "CH"
455 Toro              7042252  7031969  7034850- "50B" 7045779- "CH"
455 442             7042253  7031969  7034847- "47B" 7045779- "CH"

Notes:

The following abbreviations are used:

A.I.R. - Air Injection Reactor
C.C.C. - Climatic Combustion Control
O.A.I. - Outside Air Induction
M.T. - Manual Transmission
A.T. - Automatic Transmission
Toro - Toronado
W-30 - High-performance big-block engine
W-31 - High-performance small-block engine

(1) Except for the applications otherwise noted, the carb listed was used in all applications of that motor. The usual exceptions are the specific engines used in the 442 and Toronado models.

(2) The last two digits of the part number designate the size of the jet orifice in thousands of an inch. Thus, a jet with the part # of 7031971, has an orifice of .071", and is stamped with a "71".

(3) The last two digits of the part number usually designate the size of the largest portion of the tapered shank of the rod in thousands of an inch; Thus a primary rod with the part # of 7031844 has a taper of .044" at its largest point. This two-digit number is also stamped on the rod. After 1968, the metering rods had a double or triple taper, and had a "B" or a "C" suffix stamped on the rod, respectively. These triple-taper rods, however, do not have a part # corresponding to the size of the taper, although the stamped number on the rod does correspond to its diameter.

(4) The secondary metering rods are stamped with a two-letter code. A guide to the comparative dimensions of these rods can be found on pp. 152-153 of Doug Roe's Rochester Carburetors.

(5) The O.A.I. carburetor had the same part # as the standard manual transmission 442 engine carburetor, but had different primary metering rods.

(6) Note that the W-31 and W-30 carburetors apparently used 2-bbl jets with NO primary metering rod, and thus no power piston. If any owner of one of these carburetors could confirm this, I would appreciate it (I thought it was a typo at first, but it is specifically listed this way for both W-31 and W-30 applications).

The Doug Roe book on Rochesters, in the chart showing all the primary metering rods, shows the only triple taper rods ever made were rods 7040699- 48C and 7040701- 52C, and these were used on 1970 Oldsmobiles only. Olds was also the only one to use the triple rods.

The triple taper rod was and attempt to fine-tune the fuel curve more precisely than the dual-taper rods, introduced in 1968, allowed. I guess it didn't work well enough to justify the expense, since they went back to dual-taper rods the very next year. It seems that the carb section of the Olds engineering department was getting a lot of overtime calibrating the 1970 units, what with the triple-taper rods and the no-rod "W" units. Apparently, not everybody went to the dual-taper rods in 1968, however.

Mondello's tech guide states that the replacement of the primary metering rods is unnecessary, since they all have the same size small-end. While this is true, it is only applicable for WOT use. At part-throttle, the taper of the rod is somewhere in the jet, and it's this taper that determines part-throttle response. You know, when you want to merge or accelerate like a responsible citizen; not too cool to drive at WOT all the time when you're taking your family out for dinner. Therefore, for street use you do want to select a primary metering rod that will complement your setup.

[ Thanks to Bob Barry, Jeff Easton for this information ]
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