Editing How to rebuild a Rochester Quadrajet 4MV carburetor (section)
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====Carb gaskets==== =====Early factory intake with exposed heat crossover===== [[File:Early qjetintake1.jpg|thumb|right|350px|Arrows indicate heat passage holes which can be blocked if desired]] On early (about 1969-back) Chevy BBC and SBC Q-jet intakes, the manifold was equipped with an exposed heat crossover below the primary side of the carb. This intake manifold requires a specific gasket and heat shield (below left) be used to prevent vacuum leaks and to resist the heat. [[File:Carb gasketsearly q-jet.gif|thumb|350px|left|Metal heat shield goes against carb; fiber insulator goes against intake]] The heat crossover can be blocked either at the intake gasket, or by blocking off the ports that feed heat to the "U"-shaped channel in the intake with 1/4" pipe plugs. This mod will prevent the base plate from possibly warping and should help provide a denser air/fuel mixture due to the cooler temperature. Be aware that this can mean longer warm up times, and may require some changes to the calibrations. <br style="clear:both"/> {{Caution}}Tighten the carb to the thick insulator-type gasket evenly but not too tightly. Because the gasket of that type has a lot of give to it, it can cause the base plate to warp- sometimes enough to cause the throttle shafts/blades to bind. In severe enough cases the baseplate can even crack. =====Later factory and aftermarket intakes===== In most cases a thick fiber insulator-type gasket will provide good sealing and help to keep the carb temperature down. Heed the caution above regarding not overtightening the carb.
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