It was the double d socket. It's a QuadraJet. It should be set at 2.5 turns UP from a full bottom out. I am no expert on the Q-jet, so I'd like some thoughts on adjustment. Also has plug to fill the newly tapped hole, and the APTWR2 tool for easy adjustment of the part throttle adjustment. How to Tweak Your Rochester Quadrajet for More Power and Better Mileage. Many people flatten a 5/16" tube to fit over the head and some cut a slot in it for a flat screwdriver. Adjusting a Quadrajet carburetor requires basic knowledge behind the theory and concept of this carburetor. There are two common types of APT adjustment locations: later carbs use a plugged hole in the airhorn, earlier carbs use a plugged hole in the baseplate. You will need a 3/8 x 16 tap for the hole in the air horn. I used the brake booster vacuum line for the manifold vacuum source, and I adjusted the idle mixture screws with okay results since I did not have a decent baseline to work from. Also. The pistion has a little rod that touches the APT screw. Finally!!! APT ADJUSTMENTS – (QUADRAJET LATE MODEL ONLY) The adjustable part throttle (APT) screw can be used to fine tune the cruises (steady throttle, freeway speed) mixture. Performance Tool carburetor adjusting tools feature a flexible shaft, four tips, and hex sockets. The tips will store in the handle or the plastic boot. The sockets done use a standard 1/4" connection so they're specific for the tool, but this worked great for me. By raising/lowering the adjustment screw you will have fine control of the part throttle mixtures. You use a 3/16" hex head to turn it. It was the double d socket. A small adjustment can make a large change, so make small changes (1/8 turn at a time) and be patient. APT Plug Kit for Quadrajet Carb Tap Plug and Tuning Tool Qjet 1975-1989 . This plug is 3/8x16 thread and 3/8" long. Install the APT adjustment screw into the main casting. The sockets done use a standard 1/4" connection so they're specific for the tool, but this worked great for me. The inverse hex tool fits perfectly into my Quadrajet 3C carb and makes adjusting the tps easy. Words And Photos: Jeff Smith. Copied from W-Machines of December 1984. Item Information. The Rochester Quadrajet carburetor can still hold its own on the racing circuit with some minor adjustments and modifications - Circle Track Magazine ... and they have the APT adjustment. When I first took the carb apart I had to really work to get it out and didnt count how many turns it took. The idle screws on a Rochester Quadrajet carburetor fine tune the air-fuel ratio going into the engine during idle. This adjustment is referred to as the APT or "adjustable part throttle" setting. Use this plug for the APT access hole in the air horn on Quadrajets with internal Adjustable Part Throttle mixture screw. The next step is the primary jet. These tools adjust various settings on Rochester QuadraJet, DualJet, & VaraJet carburetors on most GM vehicles having the 3C system.Weight: 3 oz. Just what exactly does this do? Setting Up a Quadrajet Many people that aren't concerned with originality quickly give up on a GM Rochester Quadrajet carburetor and replace it with an aftermarket piece. Quadrajet Tuning: Adjusting the Idle Mixture Screws Handle is hollow and has a screw on cap that allows for convenient storage of bits in handle. A few months back, (Read it HERE) we detailed how JET Performance restored an absolutely desperate looking Q-jet to the point it looked like it had just rolled off the Chevy parts department counter back in 1970.Since carburetors have to perform better than they look, the … The APT has a rectangular head, which requires a special tool. A brass cap in the air horn was located directly above an adjustment screw and was used to fine-tune part-throttle air/fuel mixture ratios. Power Tuning a Quadrajet Carb. Thats neutral, more up is richer, lower is leaner. Other carburetors may have a 4 corner idle mix adjustment (4 idle mixture screws). Power Piston (APT) Metering Adjustment Screw Quadrajet Secondary Throttle Shaft Spring Quadrajet TPS Stem & Accelerator Pump Retainer, package of 5 Retainer - E-Clip - .125", 1/8", package of 10 Retainer (LH) Rod Clip (OEM #7003242) Retainer (RH) Rod Clip (OEM #7003137) Retainer Pin, package of 10 Retainer Pin, package of 10 The carb in the picture should have a metal pin on the front of the power piston. Its ISDN number is 0-89586-301-4 and retails for $16.95 US. Part Number: MNP-08-0229 SC made me a tool in their shop. This was exactly what I needed to adjust the 4 barrel quadrajet on my 84 Chevy 305 v-8 engine. No author mentioned. Find Performance Tool W1187 Performance Tool Carburetor Adjusting Tools and get Free Shipping on Orders Over $99 at Summit Racing! Working with a unit that is up to par, we can make metering and calibration changes to get the desired and predicted results. APT is the adjustable part throttle. Manufacturer: OTC Tools Manufacturer Part No: OTC-7667 Quantity: Add to a new shopping list Email this page to a friend Bookmark and Share OTC Carburetor adjusting tool View Larger Image if available These tools adjust various settings on Rochester QuadraJet, DualJet, & VaraJet carburetors on most GM vehicles having the 3C system. I'd recommend it to anyone who wants to rebuild or learn about quadrajet … $15.99/ea. HOOAI Carburetor Adjustment Tool Kit for Common 2 Cycle Carburator Engine - Carburetor Adjustment Tool Set Carburetor Tune up Adjusting Tool (10pcs + Cleaning Tool) … This was exactly what I needed to adjust the 4 barrel quadrajet on my 84 Chevy 305 v-8 engine. These adjusters will work on a variety of applications. The pin contacts an adjustment screw in the main casting. Thats you APT( adjustable part thottle) setting. Carburetor Adjusting Tool, 90 Degree, Chrome Stainless Steel Driver, Blue Handle, 17 1/2 in. The Quadrajet uses a Double "D" carburetor adjusting tool. Some carburetors, such as the Quadrajet found in most GM vehicles, have a special screw and require a specific adjusting tool. It was a GM Dealer only tool for many years and is hard to find at Dealers since carbs have been gone for so long. How to Adjust Idle Screws on a Quadrajet Carb by Lee Sallings . It determines a lot of rich/lean settings. I looked for a long time to find this tool. ... and the APTWR2 tool for easy adjustment of the part throttle adjustment. There is plug in the Quadrajet's cover that is removed to access the APT without having to disassemble the carb. Dealing with a 77' q-jet (from a 350 chevy truck and on a 307 now) that has the APT screw located just forward of the main metering piston. Quadrajet Tools 15x Folding Magnifier, Triple Lens 61-80 Drill Bit Set in Metal Case Carburetor Bushing Installation Kit - 3/8" throttle shafts, Quad Carburetor Bushing Installation Kit, for 5/16" Carburetor Thrott Carburetor Idle Mixture Adjusting Tool Fuel Inlet 1"-20 Threaded Insert Coils- (5 pack) The oft-maligned Quadrajet has been the victim of much verbal abuse, with such nicknames as "Quadrajunk" and "Quadrabog". Includes tap, to add threads to the hole in air horn originally filled with aluminum plug. In a nutshell, Quadrajet carburetors have different barrel sizes for its 2 primaries and 2 secondaries thus the term Quadrajet. Make sure to put the spring in first and return the APT screw to the original setting recorded when the carburetor was taken apart. First, let me presume that there is just some small adjustments that need to be made, such as the APT [I think that's what it's called] or the secondaries. Buy 2. These are the screw in babies in hole "D". Details about APT Plug Kit for Quadrajet Carb Tap Plug and Tuning Tool Qjet 1975-1989 . the screw thing in front of it is critical too. Bulk savings: Buy 1. Airhorn APT adjustment location. Length, Bits, Kit. This book is ABSOLUTLEY invaluable in doing a rebuild. I didn't have one and, as you know, one cannot have too many tools. APT plug kit. The JET Adjustable Part Throttle (APT) kit contains all the parts and tools you need to make the primary metering circuit on your Quadrajet fully adjustable from the outside. This is another tuning aid when dealing with long duration or overlap cams. Most of the later metering rods have a tapered second step. Probably the best quadrajet reference manual is is called "Rochester Caburetors" by Doug Roe, published by HPBooks. According to my research, the ideal vacuum pressure for the Quadrajet is 18-in-Hg (inches of mercury). 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