Jeep Engines - Oljeep

360 AMC V-8 (INDUCTION SYSTEM) 417After installation, some people say that their engine runsbetter with the vacuum disconnected. This is most oftencaused by the engine being too lean to begin with. Then theengine rpm will “hunt” and “wander.” The idle enginespeed will surge up and down. The engine may stall whenyou put it in gear. If it’s an automatic transmission, the idlemay drop hundreds of rpm when you put it in gear. All ofthese are signs that the engine is too lean. It needs more idlefuel. This idle enrichment cannot be done by simplyopening the throttle screw adjustment. This approach willmake it worse. To solve, richen the idle djusting screws orinstall larger primary jets. On Carter carburetors you canalso swap in smaller metering rods.Lean Idle Fuel MixtureIn high performance cars and trucks, it is a very commonproblem to have a lean idle fuel mixture in the carburetorthat you are using. This can be more common in Cartercarburetors than in Holley carburetors.Why would a lean mixture problem be more common in aCarter carburetor than a Holley? Good question! Cartercarburetors were commonly used on production enginesand were not as popular in the aftermarket. Holley was verystrong in the aftermarket. So if you have a Carter carburetorchances are it was used on a production vehicle while aHolley carburetor was probably obtained in the aftermarket.The typical aftermarket carburetor was built with a richeridle circuit. The production carburetor was built with a leanidle circuit.Within the Carter carburetor family, the AFB will have theleast problems, and the AVS and Thermo-Quads will havethe most problems. The reason is similar to the Holleycarburetor. The AFB was built up through 1967 beforeengine emissions became a bigger concern than engineperformance. Therefore, the AFB tends to be richer at idle.Fuel economy in the early 1960s was not a big concern whichalso lead to using more fuel. The AVS and Thermo-Quadcarburetors are both emissions carburetors that were built totough standards. (Emissions engines actually had much betterfuel distribution than older engines. From a technologystandpoint, AVS and Thermo-Quad were better carburetors.)Today, only the AFB carburetor is still made. Since it isprimarily made for the aftermarket, it tends to have a richeridle. There were many more AVS and Thermo-Quadcarburetors built from 1968-78 than there were AFBs from1962-67. It’s all percentages, the law of averages! There aremany exceptions. Holley makes replacement carburetorsfor emissions engines. There are also Carter AFB versionsfor emissions engines.What’s the big deal? So production carburetors are lean.The lean fuel problem is trouble to racers because it isusually not diagnosed properly. A bigger camshaft isinstalled and the engine idles poorly. Blame the camshaft!Or the heads! Or the intake! The actual solution is usuallya carburetor adjustment. More idle fuel! On oldercarburetors and aftermarket carburetors you might actuallybe able to adjust the idle by turning the idle screwadjustment-usually two, a left and a right. Typically thisidle adjustment is not adequate-it was adjusted and itdidn’t solve the problem. Some people will then assumethat idle fuel level is not the problem. In most cases, youhave to change the primary jets to larger ones. Usually oneor two steps will solve the problem.Primary jets for Holley and Carter AFB carburetors arereadily available. Jets for Carter AVS and Thermo-Quadcarburetors are not as easily found. If you only have one setof jets, then we DO NOT recommend you make anychanges. With no spare pieces or jet kits, it may be a betterchoice to swap carburetors to a Holley. If you can find a setof jets, even if they are the same size as the ones youalready have, you can drill them out (very carefully). Firstyou need a numbered drill set. (Most machine shops havecomplete sets.) Then you measure the jet size with thenumbered drills. You can also find this information in theservice manual for your engine. Measure it to be sure! Ifyou have a slight problem, go up one step. If you have a badproblem, go up two steps. A step is one number drill size.Be careful to drill the hole straight through the jet. Removeany burrs from the drill surface by hand. Save the stock jetsthat are in the carburetor so that you can go back to them ata future date. (You may not always want to race.)Carter carburetors have metering rods that are used for theidle mixture. To put a jet in you have to take the carburetorapart. You can change metering rods very easily withouttaking the carburetor apart. The problem is that it is noteasy to find richer metering rods and it is not easy to makethem if you don’t have a jet kit. For the Carter AFBcarburetor these jet kits should be readily available. If youcan find it, this is a very quick and easy way to change theidle mixture.STANDARD PRODUCTION 2150 CARBURETORADJUSTMENTS/OVERHAULA complete disassembly is not necessary when performingroutine service adjustments. In most instances, serviceadjustments of individual circuits may be accomplishedwithout removing the carburetor from the engine.A complete carburetor overhaul includes disassembly,thorough cleaning, inspection and replacement of allgaskets and any damaged or worn parts. When using anoverhaul kit, use all the parts included with the kit.Flooding, hesitation on acceleration, and other performanceproblems are in many instances caused by the presence ofdebris, water, or other foreign matter in the carburetor. Toaid in diagnosing the cause of the problem, carefullyremove the carburetor from the engine without removingthe fuel from the bowl. Examine the contents of the bowlfor contamination as the carburetor is disassembled.Refer to the proper service manual for detailed adjustmentand overhaul procedures.. ..