Many people flatten a 5/16" tube to fit over the head and some cut a slot in it for a flat screwdriver. It is impossible to exchange early metering rods with late metering rods. Buzzbom, you said "My initial timing is 20 degrees with vacuum on ported". Go back to the mix screws and see if you can improve on the vac reading. Adjust as required. After some troubleshooting, I noticed that only my left (choke side) primary venturi was flowing any fuel and the right-side venturi was completely dry. He may be reached via the Corvette Forum and I would ask him for his paper before trying to tune your Quadrajet. SC drilled a cone into this plug so that it can be removed with an ordinary wood screw. (if possible) 3. Used Quadrajet Parts; Fast idle cams, idle speed adjuster; Fast idle cams, idle speed adjuster. From my internet survey of APT adjustments, I believe that the APT may be turned out to a maximum of 8 to 8½ turns. After a few tankfuls of gas, I found that, even though I now have a working choke, it was difficult to start in cold weather and it has noticeable lean surge at part throttle. Ground is made through the carb body/engine block so only 1 wire is needed. The throttle idle screw is a slothead screw located on the driver’s side of the carburetor. Determine secondary metering rod hanger length The part number is cast into the secondary side of the float bowl and needs to be referenced for rebuilt kits … Just bolting-on the carb with its Chevrolet 350 calibration after sitting dry for 7 years, I found that it ran better than my AFB. I've also seen a kit for replacing this press-fit plug with pipe plug but I think that this is way more work than necessary for the few times the APT needs to be accessed. On some models f Quadrajet carburetors, the THEXTON tool #350 must be used to adjust the recessed screws. Adjust secondary air valve spring tension. If you plan to fine-tune your Corvette's Quadrajet carburetor, one tool you may want to have handy is a handheld tachometer.This allows you to check and adjust the vehicle's idle speed while you wrench under the hood. For instance, if you rebuild a carb and have to move the idle speed screw for whatever reason, how many turns past the point of contact with the throttle stop do you go when you reinstall it to get a baseline? This confirmed my expectation the factory used 0 turns of the APT adjustment starting point. Set desired speed with the Idle speed screw. Stamped 2372 or 2371 This is a 3 step fast idle cam. Since no specification exists for the number of APT turns of any carburetor, I presume that the factory set each carburetor individually on a chassis dynamometer when each car reached the end of the end of the assembly line. Adjust both screws equally and find the right mixture. The APT is an adjustable lower stop for the metering rods, located beside the power piston on newer Quadrajets. A pin sticks out of the side of the piston, which hits the APT stop at high manifold vacuum. After much trial and error with choke adjustments and APT adjustments, I learned that both have a great effect on cold starts. Air cleaner in place. This article is about my experience with calibrating a M4MC Rochester Quadrajet to work properly on the 225 slant six in my 1965 Barracuda. The fast-idle speed is very critical to the engine's performance during warm-up because this, along with the pull-off specification, determines the amount of "blow-off" the choke plate experiences. After screwing in my APT all the way, I found that the top of the metering rods were about 1.95" above the top of the jets. Only the newer M-series metering rods (ie, 48M, 49M, ... 55M - truck applications & Edelbrock Quadrajets) and the 50D have a tip diameter of 0.036" along with Edelbrock's . After a disc brake upgrade that dragged on way too long (several years), I found that my Quadrajet's fuel inlet wouldn't seal and the carb would overflow, likely from a rusty gas tank. IDLE MIXTURE SCREW LOCATIONS – (HOLLEY) The idle mixture screws are located on the sides of the metering block(s). If turned out this far, the metering rods would be sitting very high out of the jet so that the economy fuel mixture would be fairly close to the power fuel mixture. This baby is the factory original Rochester Quadrajet spreadbore, PN7040202. First, check to make sure both idle mixture screws are adjusted equally. Make adjustments 1/2 a turn in either direction to find the smoothest idle speed. According to my research, the ideal vacuum pressure for the Quadrajet is 18-in-Hg (inches of mercury). Sort By: Quick view Details. Since I also had a surplus Rochester Quadrajet that I removed my 1977 Pontiac in November of 1997 (for a propane conversion I completed in January of 1998), I thought I would give it a try in August of 2004. If it is used to kick the idle speed up when the a/c is on, it will be switched on from the a/c control head. Assuming you are starting with a freshly rebuilt carburetor, LG's Quadrajet tuning procedure has the following steps: Verify that that the float level is correct. It's been doing its thing for 40 years on my '70 L48 350 Monte Carlo--forever known as … Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! Screw, fast idle … 5. 322. If my 52K metering rod was adjusted the bottom of its travel (ie a diameter of 0.046") and I needed more enrichment (252.3 E-5 in² flow area), the best M-series rod would be the 52M with a leanest flow area of 253.3 E-5 in². I got the distributor through Mopar Performance (formerly Direct Connection) and it was used for performance (drag racing). Possible high fuel psi issue,q-jets dont typically like over 7psi of so max esp when hot with a worn needle & seat. Add to Cart. The HP and Ultra HP carburetors from Holley feature screw-in idle and high-speed air jets, which allow for emulsification tuning in various conditions. Yes it sure sounds like it may be a heat issue when you said the carb makes gurgiling sounds when you shut the motor down. If the part-throttle fuel mixture is nowhere close to being in the ballpark, no matter how rich the choke is set, the fuel mixture mixture will be too lean until the intake manifold is fully warm and will therefore require much gas-pedal pumping during warm-up. Quadrajet Power | sku: 55597. Adjust as required. Used Fast idle cam. 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