Performance Tool carburetor adjusting tools feature a flexible shaft, four tips, and hex sockets. The pin contacts an adjustment screw in the main casting. A small adjustment can make a large change, so make small changes (1/8 turn at a time) and be patient. It was the double d socket. Make sure to put the spring in first and return the APT screw to the original setting recorded when the carburetor was taken apart. 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. This plug is 3/8x16 thread and 3/8" long. You use a 3/16" hex head to turn it. By raising/lowering the adjustment screw you will have fine control of the part throttle mixtures. 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. Finally!!! I'd recommend it to anyone who wants to rebuild or learn about quadrajet ⦠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. Finally!!! It's a QuadraJet. 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 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. 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. APT ADJUSTMENTS â (QUADRAJET LATE MODEL ONLY) The adjustable part throttle (APT) screw can be used to fine tune the cruises (steady throttle, freeway speed) mixture. Other carburetors may have a 4 corner idle mix adjustment (4 idle mixture screws). ⢠Weight: 3 oz. This is another tuning aid when dealing with long duration or overlap cams. Adjusting a Quadrajet carburetor requires basic knowledge behind the theory and concept of this carburetor. APT is the adjustable part throttle. APT Plug Kit for Quadrajet Carb Tap Plug and Tuning Tool Qjet 1975-1989 . How to Adjust Idle Screws on a Quadrajet Carb by Lee Sallings . SC made me a tool in their shop. $15.99/ea. Thats neutral, more up is richer, lower is leaner. I am no expert on the Q-jet, so I'd like some thoughts on adjustment. 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. Thats you APT( adjustable part thottle) setting. Condition: New. 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) Power Tuning a Quadrajet Carb. This book is ABSOLUTLEY invaluable in doing a rebuild. It determines a lot of rich/lean settings. Length, Bits, Kit. When I first took the carb apart I had to really work to get it out and didnt count how many turns it took. Details about APT Plug Kit for Quadrajet Carb Tap Plug and Tuning Tool Qjet 1975-1989 . This was exactly what I needed to adjust the 4 barrel quadrajet on my 84 Chevy 305 v-8 engine. Working with a unit that is up to par, we can make metering and calibration changes to get the desired and predicted results. These tools adjust various settings on Rochester QuadraJet, DualJet, & VaraJet carburetors on most GM vehicles having the 3C system.Weight: 3 oz. These are the screw in babies in hole "D". american v8 engine image by kenmo from Fotolia.com. Includes tap, to add threads to the hole in air horn originally filled with aluminum plug. Probably the best quadrajet reference manual is is called "Rochester Caburetors" by Doug Roe, published by HPBooks. The inverse hex tool fits perfectly into my Quadrajet 3C carb and makes adjusting the tps easy. The next step is the primary jet. Airhorn APT adjustment location. Bulk savings: Buy 1. This adjustment is referred to as the APT or "adjustable part throttle" setting. You will need a 3/8 x 16 tap for the hole in the air horn. 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. Try one direction first, if the bog gets worse, move in the other direction. Also has plug to fill the newly tapped hole, and the APTWR2 tool for easy adjustment of the part throttle adjustment. Most of the later metering rods have a tapered second step. the screw thing in front of it is critical too. HOOAI Carburetor Adjustment Tool Kit for Common 2 Cycle Carburator Engine - Carburetor Adjustment Tool Set Carburetor Tune up Adjusting Tool (10pcs + Cleaning Tool) ⦠These adjusters will work on a variety of applications. It was the double d socket. Use this plug for the APT access hole in the air horn on Quadrajets with internal Adjustable Part Throttle mixture screw. Also. Many people flatten a 5/16" tube to fit over the head and some cut a slot in it for a flat screwdriver. Install the APT adjustment screw into the main casting. 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. Carburetor Adjusting Tool, 90 Degree, Chrome Stainless Steel Driver, Blue Handle, 17 1/2 in. APT plug kit. Words And Photos: Jeff Smith. 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. 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. In a nutshell, Quadrajet carburetors have different barrel sizes for its 2 primaries and 2 secondaries thus the term Quadrajet. It should be set at 2.5 turns UP from a full bottom out. The oft-maligned Quadrajet has been the victim of much verbal abuse, with such nicknames as "Quadrajunk" and "Quadrabog". ... 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. 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. Part Number: MNP-08-0229 Copied from W-Machines of December 1984. Item Information. Some carburetors, such as the Quadrajet found in most GM vehicles, have a special screw and require a specific adjusting tool. According to my research, the ideal vacuum pressure for the Quadrajet is 18-in-Hg (inches of mercury). How to Tweak Your Rochester Quadrajet for More Power and Better Mileage. The APT has a rectangular head, which requires a special tool. Just what exactly does this do? The Quadrajet uses a Double "D" carburetor adjusting tool. In addition to APT, many 1975 model-year Quadrajets received an additional power piston and single jet/rod assembly. This was exactly what I needed to adjust the 4 barrel quadrajet on my 84 Chevy 305 v-8 engine. 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. I looked for a long time to find this tool. Its ISDN number is 0-89586-301-4 and retails for $16.95 US. The idle screws on a Rochester Quadrajet carburetor fine tune the air-fuel ratio going into the engine during idle. I didn't have one and, as you know, one cannot have too many tools. Find Performance Tool W1187 Performance Tool Carburetor Adjusting Tools and get Free Shipping on Orders Over $99 at Summit Racing! The carb in the picture should have a metal pin on the front of the power piston. The tips will store in the handle or the plastic boot. 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