Upgrade your Rochester Quadrajet carburetor with our latest high performance ethanol resistant Quadrajet carburetor parts. This test is performed to ensure that all idle circuits and other carburetor functions are working properly. Make sure float doesn’t rubbing somewhere. and customer satisfaction. There should be no bubbles. Look for any fuel restriction – check for kinks in the fuel line. A Quadrajet is a unique carburetor in that it has small primary plates and huge secondary plates. QuadraJets are only slammed by people who know nothing about them. If wire doesn’t do it, try heating the outside of the passage and then blow air through. Too much fuel boils down to getting too much in the float bowl. Simple to test by loosening the gas cap after turning the engine off. Ethanol ready, made in the US and meets or exceeds manufactures specifications. Is the fast idle sitting on the higher step of the cam. First lets start by learning how to start a classic car with a carburetor. It has a spring located in the manifold with a rod running up to the plate. Many rebuilds are ruined by a dirty fuel tank, or filter. Replace any fuel filters – There is usually one in the fuel inlet of the carburetor and often there will be an in-line fuel filter. It is a good carburetor for fuel economy and still has stellar performance when required. You want to make sure the pressure is where it should be. If you see dirt in the bottom of the fuel bowl, rebuild the carburetor, clean the fuel lines & the gas tank. I don’t have these. Idle Compensator is MissingThe Hot Idle Compensator, when used on 4MC and 4MV Quadrajet carburetors (View C) is located in a chamber at therear of the carburetor float bowl adjacent to the secondary bores. 12 page 14 of the Quadrojet models 4mv,4mc carburetor manual all are connected to the air horn. NOTE: Do not apply any pressure to the needle when adjusting the float. Includes theory, diagrams, detailed specifications, tune-up data and complete overhaul procedures. The engine needs a bit of help when cold. Since the compensator part is not being produced you don’t have any choice but to run without it. Consult your repair manual for the specification, but 4 to 5 lbs is average for most carbs. Grimsrud on troubleshooting and tuning Quadrajet carburetors. This is more of an over rich condition than flooding, but flooding to one person may be different to another person. Pumping the gas a couple times can also start the engine, since the carburetor has an accelerator pump. This can be caused by several things, but there is one item often missed by the rebuilder and that is the idle tube. Rochester QuadraJet is a superior carb when tuned and set up right. Bad float – For brass floats, heat up some water to prior to boiling, then emerse the float. It is a good carburetor for up to close to 400 horsepower. Your problem is not bushings. Most carb problems are attributed to dirt. Adding an affordable vacuum gauge to your toolbox is a good idea, but you can tune your Quadrajet carburetor pretty well without one, provided the carb and the engine are in proper running condition. Be sure the throttle body gasket isn’t leaking. Inspect the choke system while the engine is cold. The cup curled, or is damaged. Free Carburetor Repair Manuals Mikes Carburetor Parts. Rochester carburetors were quite possibly the most widely used carburetor in the twentieth century, with over one million units produced by the Delco Carburetor Company, a division of General Motors. Lack of power is often caused by electrical, or engine wear. If not, pull the hose off the servo and see if the arm extends and contracts when the hose is reinstalled. Float isn’t dropping far enough to open the needle fully. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam). Top of the carburetor to the float bowl gasket may be leaking due to bad, or wrong gasket, or a warped float bowl, which is not uncommon on the Quadrajet. The choke mechanism is the plate on the top of the carburetor. My question is: Do you think I should replace the thottle body linkage bushings? It should be around the outside of the arm. A non vented gas cap on a system that needs a vent will cause gas to get siphoned out of the float bowl. If the fast idle isn’t working then the engine may die after starting. If so, then the check may be leaking. I think this is what I need to do. doesn’t have the secondary accelerating well tubes. This would indicate the main discharge, possibly the check ball, not sealing. Fuel filters are dirty, or plugged – replace any in-line filter and the filter at the carburetor fuel inlet. Carburetor is flooding.Gas is running out of the top, or you get a strong gas smell? AdvertisementClick Here to Read MoreAdvertisement Introduced at the dawn of the emissions control era of the early 1960s, the “spread-bore” Rochester Quadrajet carburetor was considered leading-edge fuel delivery technology for the time. Also watch the needle to make sure it is move straight up and down and not getting caught up. This carburetor was made by Rochester , The Rochester Products Division of General Motors was located in Rochester New York and built carburetors for GM vehicles since 1949 . On a carburetor like the Quadrajet, the idle system picks up fuel from the main fuel well. What I was referring to pickup tubes are call the main well air bleed tubes (2 inside tubes ) and secondary accelerating well tubes( the 2 outside tubes) fig. We won’t discuss here, instead we will concentrate on what problems the Quadrajet may have. Float level may be too low – set to specifications. PHOTO 3 The Quadrajet is considered a three-piece design: air horn, float bowl and throttle body. And yet another troubleshooting guide here. Its limit in horsepower applications and ability to be modified was its downfall at the racetrack when horsepower climbed. The idle mixture screws are located in the base plate for superior idle quality. Carburetor Troubleshooting Tips Tech Article Chevy. There is also a volume test if you can find the spec for that. Did you test the (brass) float for leaks? Rochester Quadrajet, 4 barrel carburetor idle. A Quadrajet is a unique carburetor in that it has small primary plates and huge secondary plates. All carburetors are installed on our test engine prior to shipping. What to look for when your Rochester Quadrajet is flooding. Some will open just slightly so it doesn’t choke out. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. When the engine has just been started, there is obviously no vacuum--so no fuel is sucked into the engine to start. We stock complete accelerator pumps, replaceable cups and springs. Using a solid gasket on a carburetor designed for the slotted gasket WILL result in hot idle issues. However, it still creates a partial choke condition. Start the engine and make sure the choke opens a quarter of the way. In your youtube video (Rochester Marine Carburetor rebuild part 3 of 3) at 4:00 you mention not usually having to take apart the thottle body to replace bushings. When getting a carb from another vehicle, whenever possible, get the factory cable bracket. Make sure the power valve moved up and down easily and there is a spring under the valve. Find Summit Racing SUM-250218 Summit Racing® Remanufactured Quadrajet Carburetors and get Free Shipping on Orders Over $99 at Summit Racing! A: There are two things that can cause a Quadrajet to leak. It needs to move up and down freely. Quadrajet Carburetor Numbers 68 and later Date Code Most Rochester built Q-jets used a four-number Julian Date code. Months can also start the engine is cold to snap shut now to... Performance four-barrel applications for almost 20 years plugged – replace any in-line filter and the extra gas and leaking! Since 2008 the manifold with a rod running up to close to 400 horsepower may... And the leaking was normal ( from a drain in the carb needed to be sure the valve! I should replace the thottle body linkage bushings is leaking ( looks like plastic,. Any choice but to run without it a hole, air will bubble out Ltd. / Leaf Group /! 400 horsepower this problem with the engine has just been started, is! 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