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. The idle screws on a Rochester Quadrajet carburetor fine tune the air-fuel ratio going into the engine during idle. $15.99/ea. The pistion has a little rod that touches the APT screw. These tools adjust various settings on Rochester QuadraJet, DualJet, & VaraJet carburetors on most GM vehicles having the 3C system.Weight: 3 oz. 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. 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. The next step is the primary jet. 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 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. Condition: New. This plug is 3/8x16 thread and 3/8" long. 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 inverse hex tool fits perfectly into my Quadrajet 3C carb and makes adjusting the tps easy. This is another tuning aid when dealing with long duration or overlap cams. Most of the later metering rods have a tapered second step. How to Adjust Idle Screws on a Quadrajet Carb by Lee Sallings . It determines a lot of rich/lean settings. 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 sockets done use a standard 1/4" connection so they're specific for the tool, but this worked great for me. I didn't have one and, as you know, one cannot have too many tools. These are the screw in babies in hole "D". Also. The tips will store in the handle or the plastic boot. When I first took the carb apart I had to really work to get it out and didnt count how many turns it took. Length, Bits, Kit. The carb in the picture should have a metal pin on the front of the power piston. I'd recommend it to anyone who wants to rebuild or learn about quadrajet … Its ISDN number is 0-89586-301-4 and retails for $16.95 US. Many people flatten a 5/16" tube to fit over the head and some cut a slot in it for a flat screwdriver. It was the double d socket. Words And Photos: Jeff Smith. Try one direction first, if the bog gets worse, move in the other direction. In a nutshell, Quadrajet carburetors have different barrel sizes for its 2 primaries and 2 secondaries thus the term Quadrajet. The pin contacts an adjustment screw in the main casting. You use a 3/16" hex head to turn it. Part Number: MNP-08-0229 Thats neutral, more up is richer, lower is leaner. Other carburetors may have a 4 corner idle mix adjustment (4 idle mixture screws). A small adjustment can make a large change, so make small changes (1/8 turn at a time) and be patient. How to Tweak Your Rochester Quadrajet for More Power and Better Mileage. I am no expert on the Q-jet, so I'd like some thoughts on adjustment. The APT has a rectangular head, which requires a special tool. APT plug kit. 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. According to my research, the ideal vacuum pressure for the Quadrajet is 18-in-Hg (inches of mercury). ... and the APTWR2 tool for easy adjustment of the part throttle adjustment. Just what exactly does this do? Power Tuning a Quadrajet Carb. Airhorn APT adjustment location. In addition to APT, many 1975 model-year Quadrajets received an additional power piston and single jet/rod assembly. 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. Performance Tool carburetor adjusting tools feature a flexible shaft, four tips, and hex sockets. This was exactly what I needed to adjust the 4 barrel quadrajet on my 84 Chevy 305 v-8 engine. HOOAI Carburetor Adjustment Tool Kit for Common 2 Cycle Carburator Engine - Carburetor Adjustment Tool Set Carburetor Tune up Adjusting Tool (10pcs + Cleaning Tool) … 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. the screw thing in front of it is critical too. Use this plug for the APT access hole in the air horn on Quadrajets with internal Adjustable Part Throttle mixture screw. By raising/lowering the adjustment screw you will have fine control of the part throttle mixtures. This adjustment is referred to as the APT or "adjustable part throttle" setting. 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. There is plug in the Quadrajet's cover that is removed to access the APT without having to disassemble the carb. The oft-maligned Quadrajet has been the victim of much verbal abuse, with such nicknames as "Quadrajunk" and "Quadrabog". It's a QuadraJet. Install the APT adjustment screw into the main casting. Thats you APT( adjustable part thottle) setting. Copied from W-Machines of December 1984. Some carburetors, such as the Quadrajet found in most GM vehicles, have a special screw and require a specific adjusting tool. This book is ABSOLUTLEY invaluable in doing a rebuild. It should be set at 2.5 turns UP from a full bottom out. american v8 engine image by kenmo from Fotolia.com. Details about APT Plug Kit for Quadrajet Carb Tap Plug and Tuning Tool Qjet 1975-1989 . These tools adjust various settings on Rochester QuadraJet, DualJet, & VaraJet carburetors on most GM vehicles having the 3C system.Weight: 3 oz. 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. 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. Find Performance Tool W1187 Performance Tool Carburetor Adjusting Tools and get Free Shipping on Orders Over $99 at Summit Racing! Buy 2. SC made me a tool in their shop. No author mentioned. 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. Make sure to put the spring in first and return the APT screw to the original setting recorded when the carburetor was taken apart. Probably the best quadrajet reference manual is is called "Rochester Caburetors" by Doug Roe, published by HPBooks. Bulk savings: Buy 1. Also has plug to fill the newly tapped hole, and the APTWR2 tool for easy adjustment of the part throttle adjustment. It was the double d socket. You will need a 3/8 x 16 tap for the hole in the air horn. Finally!!! APT is the adjustable part throttle. APT Plug Kit for Quadrajet Carb Tap Plug and Tuning Tool Qjet 1975-1989 . Includes tap, to add threads to the hole in air horn originally filled with aluminum plug. The Quadrajet uses a Double "D" carburetor adjusting tool. Carburetor Adjusting Tool, 90 Degree, Chrome Stainless Steel Driver, Blue Handle, 17 1/2 in. • Weight: 3 oz. 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. Working with a unit that is up to par, we can make metering and calibration changes to get the desired and predicted results. Adjusting a Quadrajet carburetor requires basic knowledge behind the theory and concept of this carburetor. Finally!!! I looked for a long time to find this tool. The sockets done use a standard 1/4" connection so they're specific for the tool, but this worked great for me. This was exactly what I needed to adjust the 4 barrel quadrajet on my 84 Chevy 305 v-8 engine. Item Information. These adjusters will work on a variety of applications. Should have a tapered second step mixture ratios APT or `` adjustable part throttle adjustment some,. Metering rods have a special screw and require a specific adjusting tool, but this worked great for me was... Other carburetors may have a metal pin on the front of it is critical too with long or... 4 idle mixture screws ) will need a 3/8 x 16 tap for the Quadrajet 's cover that removed! 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