I am trying to find out what the factory settings or specs would be for a 70 Stage 1 Q-Jet carb. Cliff R. stated that the primary jets were .73 and the metering rods were 45Bs. Does anyone know what the secondary rods and hangers would be? Any and all help is greatly appreciated. Cliff
Cliff, when you PM'd me, you stated that you were using a 7043240 carburetor and wanted the specs for that set-up. The 1970 Stage I carburetor is not the same carburetor and may not use the same jetting. It's been a while since I've done one of those, so can't remember what jet/rods, etc they came with. I base the jetting we use here on how the carburetor is set up anyhow (airbleed "package"), and seldom use the factory jetting. We also have to alter the calibrations 99 percent of the time since it's very rare to see a factory engine in stock form. In almost all cases, folks change the cam, compression, exhaust, intake, remove emission control devices, cooler thermostat, block off heat crossovers, etc, etc. This requires calibration changes to the carburetor in one or more areas. This new fuel also contains less energy, so we compensate for that as well.....Cliff
First, in 1970, the Stage1 carburetor was 7040246. It was a 750 CFM carburetor. It used .068 jets and 42B primary rods. Secondary rods were AU's Starting in 1971, all Big block Q-jets were 800 CFM. They had bigger primaries, and were jetted richer. A 7043240 was a 1973 455 carburetor, so it was an 800 CFM. You cannot use 1970 jetting for the bigger 1973 carburetor.
Greg Gessler has a nice selection of Q Jet parts. http://www.gesslerheadporting.com/g...b85217656bd1a839852574fd005f568c!OpenDocument
"Starting in 1971, all Big block Q-jets were 800 CFM. They had bigger primaries, and were jetted richer." They used larger jets, but were not "richer". The later 800cfm carburetors had quite a bit more emulsion air. Quite a few Old's, Buick and Chevrolet q-jets produced in the late 60's and early 70's used very small main jets, as did Marine Quadrajets. They also used very small airbleeds in the main system with those jets to compensate. This is why it is not possible to utilize the calibration of the later units into the early castings (or visa-versa) without duplicating the entire calibration that those carburetors used. You would also have to alter it some since they did use larger castings on the 71-74 455 Buick carbs as noted. If Cliff F. is going to use the 7043240 carburetor on a 1970 455, it will work fine. It may need slightly recalibrated, but not using any of the specs of the original 7040246. The 71-74 240 carburetors are quite lean at part throttle, and some are a bit lean for idle fuel delivery as well. To use one effectively on a 1970 455 engine, or any high compression 455 with a decent size cam in it, it will need a different idle fuel calibration, and a tad more fuel from the primary side as well.....Cliff
