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Jets and Metering Rods
Carburetor Jets and Metering RodsHere 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:
(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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