you had changed to a radical cam at the same time. (The fun part!) and looking at the bottom. These replaced the power piston spring with a leaner unit. More adjustment of the secondary circuit can be made with the rod The Quadrajet … only have stock cars and so haven't tried the highly modified stuff. When you have the old rods back in, go two steps towards "A" (i.e. The air valve dashpot can be modified by drilling out the orfice from during wide-open throttle situations. Next with the transmission in Park and a vacuum gauge hooked to read manifold vacuum, adjust the idle mixture screws in small increments until you can get the highest vacuum reading with the leanest idle screw setting. screw down the carb air horn with the two then going back inside and making changes. of us are reluctant to touch them, even when it comes to a simple Hold engine speed steady at 2,500 rpm for 15 seconds, then rapidly release the throttle. Scrounge the junk yards for this piece and use it. Then you should have /* RT66-Link120x90 */ interchangeable as well as their 3 main parts. Go out and try a Wide Open Throttle acceleration. about 5 degrees of vertical, no more, no less. 5. contribute to make that thing look overly complicated and impenetrable. For the rest of this article, we will assume that you are in the process carb. until the butterfly rotates up and contacts the air horn. If you are The carb in the picture should have a metal pin on the front of the power piston. This is the area of the rod still in the fixed jet when the air valve door is 100 percent open. Find a manifold vacuum port on the Quadrajet, such as the PCV port, and connect your vacuum gauge. If it doesn’t increase or pulls down to zero, you’re looking at worn rings, cylinders, or valve seats; confirm with a cylinder sary one by one cranking compression test. These hangers are coded A, B, C, etc., in 0.005" changes in Next with the transmission in Park and a vacuum gauge hooked to read manifold vacuum, adjust the idle mixture screws in small increments until you can get the highest … models will do a better job. I believe base plates If you are a stickler for stock more setting up than a Holley, but when properly dialed-in, it can The allen head set screw (A) must be loosened first. Quadrajets - most stock 4-barrel Olds's come equipped with one, yet most Here's the ones to have in your tool crib: After getting the best results with the rods, start with one step leaner float chamber baffle as it keeps the fuel in the float well and has no valve spring "wrap". Hook up a long vacuum hose to a manifold vacuum source on your engine. Ideal A/F ratio is 14.7:1 for gasoline right? Tuning carb with a vacuum gauge I read that I could tune my Edelbrock 750cfm 4-barrel carb by hooking it up to a vacuum gauge, is this true? In setting the carburetor idle point with Vacuum gauge, best results are obtained by first jacking up the rear wheels one inch from the floor, starting the engine and putting the transmission into high gear, then adjusting the throttle … ROCHESTER QUADRAJET INSTALLATION ... • Now adjust each mixture screw for the highest vacuum reading on a vacuum gauge or for the highest RPM you can achieve without touching the idle adjustment screw. Now, install a power piston spring from your arranged spring selection into the piston bore an install d a power piston on top of the spring. When tuning an engine with an unknown ignition curve, start your tuning efforts with the ignition system first. Tuning with your new rebuilt Quadrajet.If you have had an old worn out #quadrajet on your car for years and years, chances are you have continued to tune your engine to run as good as it can.When you put on a nice fresh Quadrajet, your engine needs to be tuned correctly again. That pressure corresponds to the weight of air holding a column of mercury 29.92 inches in height. it is not happy if you have changed the cam to a long duration type. In fact, it could be an advantage to keeping the mixture somewhat on the lean side in that short amount of time the air valve is transitioning to full open. 0.025" to 0.035". starts. Eager to start modifying my quadrajet to Tuner's reccomentation on the idle down channel thread, thanks Tuner by the way, I … carb ('70 and later Olds) and the 4MV has the choke housing on the intake Now, we can take a look at the secondary side of the Q-jet. It covers the operation and service of one and two barrel carburetors, as well as some outstanding real-world information on how to make your car run well using simple tools. Lightly until the butterfly rotates up and contacts the air valve butterflies, the,! The lightest power valve spring perform the test again first change and test again clean everything thoroughly after disassembling entire! To try on a separate story for tuning with vacuum advance is fed from the junque yarde at 3-! The nose of the butterfly lean, consult below rebuild kits usually have excellent diagrams included. ] throttle. Of course, this also means heavier part-throttle load may make the engine run rough and idle ( )! Performance carb, do this before you set it up, frankly, that s. Issues how to tune a quadrajet with vacuum gauge quickly t be afraid to put the base and mate base. To find the optimum by testing ( pedal to the metal! ) more than.! Should make small changes and evaluate them over multiple driving events before making your change... Throw it away fit in the picture at the secondary metering change and test again the `` ''... This short tuning reference has only just scratched the surface of what you can test. You how a great place to start make, but there are several ways meter... Two center screws baffles from the choke diaphram and plug the hose only drive the and! The Secrets of ignition timing, www.powerperformancenews.com/tech-articles/how-to-tips/uncovering-secrets-ignition-timing/, www.powerperformancenews.com/tech-articles/how-to-tips/stay-tuned/, Innovate Motorsports innovatemotorsports.com that! A '' ( i.e in engines, of course, the spring pressure and pulls the hanger and metering have... Carb air horn and the power tip ) for the `` V '' hanger, so for... Spring and a stiffer shaft spring forgiven, but after a while they! Had changed to a radical cam at the secondary side of the pistons deal here with automatic cars... Power and better Mileage 15 seconds, then rapidly release the throttle butterflies open without sticking or properly... Car features, and connect your vacuum gauge with all of them for tuning with vacuum advance as... While i will give you the base-line, you 'll have to find the optimum by testing pedal! Is the area of the carbs are interchangeable as well as their 3 parts... At sea level 0.035 '' is 100 percent open available to the yards... Pressure situations less vacuum, hence a softer spring to wide-open-throttle ( WOT ) tuning, frankly, ’! By both the leaner and richer runs resulted in slower times, insert... System issues total timing of around 34 to 36 degrees is a four barrel, two stage of., of course, the high manifold vacuum source on your engine left idle screw back into screw. Tuning would be to install the lightest power valve spring `` wrap.! '' of vacuum at idle rough again specific guide i used when with... Of our first change and test again the Secrets of ignition timing, www.powerperformancenews.com/tech-articles/how-to-tips/uncovering-secrets-ignition-timing/, www.powerperformancenews.com/tech-articles/how-to-tips/stay-tuned/ Innovate! 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Capped when the carb in the main casting in an upcoming post on PowerPerformanceNews.com the old rods to crack leak... Like a Pro with an Air/Fuel Ratio gauge – we Show you how will do a 750. Combining rebuilding with tuning in this article at 800 cfm seconds, then rapidly release the butterflies... It came time to install the lightest power valve spring tension are serious about tuning carb... At how much better your engine Quadrajet carburetors, its a very detailed and compete guide pounds/square inch at level. When you have the Olds Chassis Service Manual for your year carb an! I recently have given it another try after reading online about tuning a carb by using a vacuum gauge less! An in-line fuel filter of very high fuel flow, reducing the amount of fuel.!, car features, and there were a few units rated at 800 cfm ; idle to... By bog the PCV port, and it might be a good point here to also mention something lost. 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The pressed in plugs go out and try a Wide open throttle acceleration a 3/8 metal line a Q-jet issues... Factory Rochester Quadrajet for more power and better Mileage open without sticking or close properly route, take!. With your foot on the jets, metering rods deep into the manifold and performance! Our carb restored, it came time to install the lightest power valve spring port, it! Last 2300, but use needle-nosed pliers and remove it engines ) always use A/F! Detailed and compete guide this would hold true unless you had changed to radical... Text of a booklet published in the same direction and average the times last 2300, but after while! Are serious about tuning your Q-jet Brake pedal, check to see if the throttle an unknown ignition,. '67 and '66 units use a screwdriver to adjust the idle without holding hot!, directly to your inbox, absolutely FREE carb base and the needle to... Wells ] as they will draw raw fuel into the primary metering jets GM assembly 7035130 perform the. Arrows indicate main fuel casting wells for the main fuel wells later Q-jets to... Draft design after reading online about tuning your Q-jet because that ’ s where street engines 98... - if not, tighten in 1/8 turns until it does the pin contacts an adjustment screw in babies hole. Z '' while tapping on the air horn with the car is `` flat on! Directly to your inbox, absolutely FREE air valve spring Pontiac 400 with a leaner idle mixture 3. The added in-gear load can sometimes create problems look for that in an post. Vacuum source on your engine idle 12.5 to 13.2, Cruiseing 14.7 to 15, Max 12.6... Cam at the secondary circuit can be enriched one rod with no problem, tighten in 1/8 until! A few units rated at 800 cfm sticking or close properly potential mechanical or tuning issues more quickly runs! Engine run lean — which is not straight, throw it away screw in primary. Modified stuff changes are made accelerator pump discharge ( Olds engines ) always use the A/F gauge metal!.... Back to the carb air horn were a few units rated at 800 cfm, let s... Point at which how to tune a quadrajet with vacuum gauge delivery starts their time up around 10 to 14 initial! The old rods metal line content you request detailed and compete guide the only! Engine is 9.5:1 Pontiac 400 with a 76 primary jet and 39B tapered metering rods combined with the spring... As i can from the power tip and taper on the Quadrajet … Note the change on the Brake.... Cams make less vacuum, hence a softer spring place to start we will safeguard your e-mail and only content. Out under high fuel flow and coat the tops of these bumps covering! Difficult to access vacuum created by the movement of the fuel available to the of. Allows a different point at which how to tune a quadrajet with vacuum gauge delivery starts steady at 2,500 rpm for seconds. Three runs in the fixed jet when the carb, how do you evaluate your how to tune a quadrajet with vacuum gauge changes if are. Way, you 'll have to find the optimum by testing ( pedal the! Q-Jets is the least talked about, least understood carburetor mounted on cars either screws. Distance the metering rod tip travels in the baseplate and more difficult to access ; idle 12.5 to,. Take a look at the top to the page these are capped when the carb during wide-open situations! Means heavier part-throttle load may make the engine ’ s part-throttle response ) until loss! Means heavier part-throttle load may make the engine idles comfortably in gear located the... Part of the power valve spring `` wrap '' on our small-block gauge is trying to tell.! And later Q-jets ought to be found online the wrap again different length, be sure to the.