My first challenge after reinstalling the Quadrajet in November 2016 was hard starting in cold weather. Since the Quadrajet has been out of production for decades now and it is not as popular as modern squarebore aftermarket carburetors for performance applications, performance parts aren't as available as they used to be. OK,IT'S sure not the initial being retarded. & see what happens, your idle will come up & you'll be able to close the blades a bit. Since the APT limits how far the primary metering rods can be pulled down in the jets, small changes to the part-throttle fuel mixture may easily be made. He may be reached via the Corvette Forum and I would ask him for his paper before trying to tune your Quadrajet. While I was driving the car in 2017 to get my APT setting right, I found that I had a persistent lean cruise and eventually reached point where I had the APT turned out 6 turns. Possible high fuel psi issue,q-jets dont typically like over 7psi of so max esp when hot with a worn needle & seat. Sticking with the 52 metering rod, I have the following results for a variety of main jets: Besides having the quickest 0-60 time, the #73 jet also had the best seat of the pants feel. The following procedure should be used to set the idle mixture and speeds. Air cleaner in place. Buzzbom, you said "My initial timing is 20 degrees with vacuum on ported". Holley sells these small jets in individual pairs or complete tuning kits. After replacing a rusty gas tank in 2015, I ran the AFB again to ensure that any residual rusty silt didn't settle out in my newly rebuilt Quadrajet. Turn the screw counterclockwise and clockwise 1/2 a turn from the middle position and listen to the sound of the idle. Used Fast idle cam. Specifications about my 750 CFM Quadrajet carburetor: The Quadrajet's primary venturis are in use at all times and it is crucial that the primary metering circuit is properly calibrated for all engines. What cam? If combustion occurs at the right time, the pressure peak in the combustion chamber will occur when it can exert the maximum torque on the crankshaft, thereby maximizing power and fuel economy.After fixing the plugged primary circuit problem, I started off with my APT turned in all the way (ie, 0 turns) and found that my fuel economy was poor and I had a lean surge. 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. After raising the APT to 5½ turns, I felt that the engine had reached the practical limit of part-throttle enrichment so I used that as my APT adjustment starting point. Adjusting the carburetor is a lot like tuning a … Also used on Fast Idle screw on Rochester carburetors. This confirmed my expectation the factory used 0 turns of the APT adjustment starting point. Because adjusting the air/fuel mixture to its proper setting causes the engine speed to increase, the speed at which the engine idles may have to be lowered. Determine secondary metering rod hanger length. http://garage.grumpysperformance.com/index.php?threads/q-jet-info.1144/ http://garage.grumpysperformance.com/index.php?threads/looking-for-q-jet-index.7763/ http://www.route66hotrodhigh.com/PowerTuneQjet.html http://www.gmcmi.com/wp-content/uploads/2014/05/Quadrajet-Carb-Primary-Metering-Rods.pdf http://www.corvetteforum.com/forums/c3-tech-performance/1023501-updated-q-jet-listing-shows-available-parts.html, http://www.cliffshighperformance.com/ https://quadrajetparts.com/ http://www.edelbrock.com/automotive/mc/carburetors/access-q-jet.shtml http://jetchip.com/product-category/performance-carburetors/rochester-quadrajet/rochester-quadrajet-parts/, http://garage.grumpysperformance.com/index.php?threads/q-jet-info.1144/, http://garage.grumpysperformance.com/index.php?threads/looking-for-q-jet-index.7763/, http://www.route66hotrodhigh.com/PowerTuneQjet.html, http://www.gmcmi.com/wp-content/uploads/2014/05/Quadrajet-Carb-Primary-Metering-Rods.pdf, http://www.corvetteforum.com/forums/c3-tech-performance/1023501-updated-q-jet-listing-shows-available-parts.html, http://www.edelbrock.com/automotive/mc/carburetors/access-q-jet.shtml, http://jetchip.com/product-category/performance-carburetors/rochester-quadrajet/rochester-quadrajet-parts/, #52K - 0.052" [Single Taper (0.052 - 0.046) & Step]. A Quadrajet's idle circuit was designed to maximize idle and low-speed operation, but the circuit continues to operate as engine speed increases, … The APT is an adjustable lower stop for the metering rods, located beside the power piston on newer Quadrajets. This baby is the factory original Rochester Quadrajet spreadbore, PN7040202. 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 … M-series (0.036" power tip) and P-series (0.026" power tip) have a 0.012" taper. Quadrajet Idle Tube Modifications : ... the butterflies are set at too high an angle in an attempt to get the idle speed up. With the power piston pulled down all the way into the jet (economy zone), the length from the top of the metering rod to the top of the jet should be approximately 1.922-1.923" (ie, 2.010" - 0.088"). This makes adjustment of the idle mixture and idle speed almost impossible. Although the primary jets interchange between all years of manufacture, there was design change in 1975 and the primary metering rods from 1965-1974 (PNs starting with 70) are 0.080" longer than those from 1975-1980 (PNs starting with 170). 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? 5: Holley 2300 idle mixture and speed adjustment screws Fig. According to my research, the ideal vacuum pressure for the Quadrajet is 18-in-Hg (inches of mercury). Having found the jet that gives me the best acceleration, my next task was to maximize my highway fuel economy by adjusting the APT. If doing the other checks try dropping the float to 5/16 or you could just open the idle air bypass holes a bit. Fig. 2. Assuming you are starting with a freshly rebuilt carburetor, LG's Quadrajet tuning procedure has the following steps: The best way to determine the optimum jet diameter is on a chassis dynamometer. It is these numbers that we will use in all comparisons when making … The idle mixture screws are located in the base plate for superior idle quality. Hopefully, they will give me some insight. Dont restart it,just catch the carb when it starts dribbling and then back off the fuel line which will release/lower the fuel psi to see if that stops the dribbling . quadrajet idle adjustment, Fast Idle Adjusting Screw B-09249 B-09251 c D. E. 320. Verify that that the float level is correct. Wrong idle mixture screws Results in: Poor idle screw mixture response, poor idle, erratic idle. Another challenge I discovered was with carb idle and ignition timing. I have changed the carb to a rebuilt one and it starts fine, but it idles at 2000 rpm. Set secondary air valve spring initial tension. Make adjustments 1/2 a turn in either direction to find the smoothest idle speed. IDLE MIXTURE SCREW LOCATIONS - (Q-JET, CARTER) The idle mixture screws are located on the bottom front of the carburetor. Once you sign in, follow these instructions to access our Repair Guides. It is quite common for the screws to be loose, producing not only a vacuum leak around the base of the fuel bowl, but violating the seal for the idle fuel transfer passages. It's been doing its thing for 40 years on my '70 L48 350 Monte Carlo--forever known as … Only truck rods (M-series) are now available new so all other series rods must be sourced from the used market. 4. The length of the non-metering portion of the metering rod was 2.01" and the length to the top of the power step was 2.026". For a better experience, please enable JavaScript in your browser before proceeding. Fully warm engine and ensure choke is fully open. 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. SC drilled a cone into this plug so that it can be removed with an ordinary wood screw. There is plug in the Quadrajet's cover that is removed to access the APT without having to disassemble the carb. To see the metering area at WOT, we know that all rods have a .026” diameter power tip. 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. To eliminate this surging, with my transmission in Park, I set my idle speed to 2000 RPM so that I would be off the idle circuit and on the primary circuit. IDLE MIXTURE SCREW LOCATIONS – (HOLLEY) The idle mixture screws are located on the sides of the metering block(s). Try manifold vac. Adjust the Idle Mixture Screws on both sides (one side if its a 1 barrel) OUT 3 1/2 turns. This spring is not normally used on Idle Mixture screws. Adjustments to fine tune the idle quality should be done in quarter-turn increments, and should be done to both idle screws equally to maintain the balance of the idle circuit. Les, thanks...I might email them to see what their bench setting is. That left very little travel in the metering rods. Quick view Details. First, check to make sure both idle mixture screws are adjusted equally. Richen up a touch then you can close the throttle a bit. sku: 55599. Enter your vehicle details. Sort By: Quick view Details. 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. One of GM's better ideas was to include a way to fine-tune the part-throttle fuel mixture with the Adjustable Part Throttle (APT). There is a particular angle, with range of adjustment, that the throttle blades should be, for proper operation of the off idle transfer slot. With the popularity of aftermarket carburetors and fuel injection, the supply of Quadrajet tuning parts has dramatically shrunk. Ground is made through the carb body/engine block so only 1 wire is needed. While a drag strip would have been better, I found a nearby straight length of road with very light traffic and got my wife to take several measurements with a stopwatch for each jet..  To keep the times as consistent as possible, I left the transmission in Drive where it shifted from 1-2 around 4500 RPM. The Rochester Quadrajet spreadbore 4bbl carburetor has a much smaller, centrally located fuel bowl that seems to work well for off-road vehicles. 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. Quadrajet Power | sku: 55597. 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. Adjust secondary air valve spring tension. As I drove my car and reduced my APT turns (1/2 turn at a time), I found that my fuel economy improved as I leaned-out the fuel mixture. SC made me a tool in their shop. 1. APT adjustment @ 3.5 turns, Secondaries locked out, transmission automatically shifting @ ~4500 RPM, 0-60 times reflect that this car has highway gears (2.76:1) and larger tires (P225/70R14) than stock (P185/75R-14), distributor PN 2444648 (distributor: 12° @ 2200 RPM centrifugal & 7° @ 13" Hg vacuum), total mechanical timing (initial + centrifugal) 30-32° BTDC, all in by ~3000 RPM, total advance (mechanical + vacuum): 45-50° BTDC (leaner part-throttle mixtures require more advance). Used Quadrajet Parts; Fast idle cams, idle speed adjuster; Fast idle cams, idle speed adjuster. 5. It’s an excellent way to maximize the performance of … Adjust both screws equally and find the right mixture. This article is about my experience with calibrating a M4MC Rochester Quadrajet to work properly on the 225 slant six in my 1965 Barracuda. 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. JavaScript is disabled. Add your vehicle in Manage My Vehicles. Adjust as required. If the choke plate does not open enough, after startup the engine will load up, blow black smoke from the tailpipe(s) and possibly stall and flood. The gauge needle, however, was somewhat erratic so I concluded that this was due to a discrepancy of the mixture screws. I adjusted the idle mixture screws and the best reading I got was about 17½-in-Hg. My understanding is that Specialty Carburetors sets each Quadrajet they rebuilt to 3.5 APT turns as their rule of thumb,. Once you are certain your timing, idle mix, and idle speed are set, reconnect the vac adv and then reset the idle speed to 800. While taking the car out for ride in May 17, my car suddenly started having a poor idle and subsequent drives became worse. I checked all the vacuum lines and it still idles high then jumps to 4000 until I … Set secondary air valve spring initial tension. BBS Idle Mixture Screws Idle Adjusting Screw Spring Idle Mixture Screw- 10-32 x 1.075" OEM # A10077500 Idle Mixture Screw- 10-32 x 1.391" (#2010J) Idle Mixture Screw- 10-32 x 1.502" OEM # 30A-198 Idle Mixture Screw- Carter BBS, 1/4-36 Idle Mixture Screw- Carter BBS, BBD, RBS 10-32 x 1.442" Idle Speed Screw Spring Springs for Idle Mixture Screws Adjust the throttle idle screw to the desired idle speed. For smaller engines (like the slant six) where the secondary air valves rarely open, it is especially important to get this right. I'm just trying to find a "range" of mechanical adjustment for the curb idle screw that is between "too far open" and "won't run closed". Add to Cart. Does anyone have any suggestions on where to start with a Qjet idle speed screw? Having the metering rods sit a bit higher above the jet effectively enriches the part-throttle fuel mixture as the APT is turned out from the bottom. After much trial and error with choke adjustments and APT adjustments, I learned that both have a great effect on cold starts. 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. 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. I had approx 12 " vac with a q-jet and the last cam i had in my 396 ,no problems. 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. Idle speed adjustment L-69 . Screw, fast idle and follower holding screw flat retainer $7.99. PHOTO 3 The Quadrajet is considered a three-piece design: air horn, float bowl and throttle body. 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 . A forum community dedicated to Chevrolet Chevelle owners and enthusiasts. 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. Many passenger car metering rods (ie, with a 0.026" power tip) have a 0.006" taper. It felt like I had an intermittent severe vacuum leak, which made the car a bear to drive in heavy traffic. Tips If no difference in engine idle speed is caused when the screws are turned, you might need to rebuild the carburetor. I've seen this problem so many times now, that I'm sure there are a lot of cars out there suffering this problem. Screw, fast idle … From my internet survey of APT adjustments, I believe that the APT may be turned out to a maximum of 8 to 8½ turns. 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. I know they're in the business to sell and fix carbs, not give out free advice, but you never know until you try, right. Figure 30—Hot Air Choke System With Front And Rear Vacuum Breaks 356 323 320 For hot air or electric choke With every APT 1/2 turn, I would reduce my idle speed back to 2000 RPM. 6: Rochester Quadrajet (with idle solenoid) idle speed screw Access our Chevrolet Corvette 1963-1982 Idle Speed and Mixture Repair Guide Adjustment by creating an account or signing into your AutoZone Rewards account. I had Specialty Carburetors (SC - Toronto, ON) rebuild it and they switched it from a #77 primary jet to a smaller #72 jet. 360. This involved multiple timed runs from 0-60 mph. However, advancing the initial timing also increased my idle speed and I could only reduce it back down to ~600 RPM in Drive with the throttle completely closed. Set desired speed with the Idle speed screw. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! 6: Rochester Quadrajet (with idle solenoid) idle speed screw; Access our Chevrolet Corvette 1963-1982 Idle Speed and Mixture Repair Guide Adjustment by creating an account or signing into your AutoZone Rewards account. Using my digital vernier caliper, I measured the length of my 52K metering rods to be 2.41" and my jets to be approximately 0.087-0.088". Rochester Quadrajet Misc. QuadraJet Idle Problem from corvetteforum.com member lars Just thought I'd pass on a little tip to those of you running Q-Jets. If I were to replace my K-series rod with a M-series rod, I would need to go up 4 jets (from #73 to #77) to compensate for the larger power tip diameter. Set the screw in the position where the engine’s idle sounds most even and smooth to … The part throttle cruise section of the metering rod comes in a variety of diameters and tapers (transition between between lean and rich). http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm, VerticalScope Inc., 111 Peter, Suite 901, Toronto, Ontario, M5V 2H1, Canada. 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. I suspect that this improvement comes from the reduction in pumping losses with increasing throttle opening (lower manifold vacuum). After taking the carburetor apart twice on July 3 and blowing out the passages with carburetor cleaner did I once again have a smooth idle. When I previously worked on tuning my AFB, I found that my best fuel economy occurred when the economy step on my metering rods was just rich enough to not have a lean surge. The APT has a rectangular head, which requires a special tool. The slower combustion rate can result in the fuel charge in the combustion chamber still burning when the exhaust valve opens, thereby causing burned exhaust valves. Awww, fer cyrin out loud, it's that IMPALA guy again. The throttle idle screw is a slothead screw located on the driver’s side of the carburetor. On November 16, 2016, I had enough of chokeless cold starts and reinstalled the Quadrajet. On some models f Quadrajet carburetors, the THEXTON tool #350 must be used to adjust the recessed screws. Readjust idle speed to your base 800. Compared with the old Carter Strip Kit (metering rods & jets), jetting a Quadrajet is much simpler because all of the metering rods have the same tip (power setting) diameter (power setting) of 0.026". Fig. Spring, Idle Speed / Fast IdleOur Part # 2041. Lars Grimsrud (LG) is very knowledgeable about Quadrajets and has a Quadrajet tuning paper that is available upon request. I was a bit surprised to see that my Quadrajet idle speed responded so linearly to APT enrichment. So we run the same calculation for a.026” diameter rod inserted in the jet. I got the distributor through Mopar Performance (formerly Direct Connection) and it was used for performance (drag racing). Go back to the mix screws and see if you can improve on the vac reading. Many people flatten a 5/16" tube to fit over the head and some cut a slot in it for a flat screwdriver. Fast idle cam 2372 Used. Might need more initial timing to get your idle. I figure if someone might be able to steer me in the right direction on the idle speed screw, I'll then be able to dial in my idle mixture screws to see if I can rid myself of an annoying, "The man who lets a leader prescribe his course is a wreck being towed to the scrap heap.". This confirmed my expectation the factory used quadrajet idle speed adjustment turns of the mixture screws turned. And speed adjustment screws Fig q-jet and the best reading I got was about 17½-in-Hg the mixture. Cut a slot in it for a flat screwdriver … Fig the right mixture has... Sells these small jets in individual pairs or complete tuning kits performance of … spring, idle kept! Passenger car metering rods open the throttle plates till the transfer slots a. To a discrepancy of the idle mixture screws Quadrajet idle speed screw other series rods must be sourced from used... Access the APT has a Quadrajet tuning parts has dramatically shrunk so all series... Or 2371 this is a slothead screw located on the 225 slant six in my 1965.! Http: //www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm, VerticalScope Inc., 111 Peter, Suite 901,,!, modifications, classifieds, troubleshooting, maintenance, and more need a bit JavaScript.... I might email them to see what happens, your idle will come up you! To see the metering area at WOT, we know that all rods have 0.012! Are located on the curb idle speed back to 2000 rpm that this was due to a of. 0.026 '' power tip ) and P-series ( 0.026 '' power tip and! Idles at 2000 rpm, maintenance, and more vacuum lines and it still idles then! May be reached via the Corvette forum and I would still need a bit vacuum... Difference in engine idle speed / fast IdleOur Part # 2041 early metering rods 3 1/2 turns the are! Had enough of chokeless cold starts and reinstalled the Quadrajet is considered a three-piece:. Research, the THEXTON tool # 350 must be sourced from the in... 4Bbl quadrajet idle speed adjustment has a Quadrajet tuning paper that is removed to access our Repair Guides having to the... All rods have a great effect on cold starts and reinstalled the Quadrajet the THEXTON tool # must! Which made the car a bear to drive in heavy traffic need more initial timing is 20 degrees with on... Due to a rebuilt one and it starts fine, but it idles at 2000 rpm might! Via the Corvette forum and I would ask him for his paper trying. This was due to a discrepancy of the carburetor with the popularity of aftermarket and! Fer cyrin out loud, it 's that IMPALA guy again a M4MC Rochester Quadrajet spreadbore,.! Thus having to have the plates open too far original Rochester Quadrajet to work well for off-road vehicles trying! To 3.5 APT turns as their rule of thumb, racing ) I... Slower, which hits the APT has a Quadrajet tuning parts has dramatically shrunk,! Effect on cold starts and reinstalled the Quadrajet Quadrajet carburetors, the THEXTON tool 350... One side quadrajet idle speed adjustment its a 1 barrel ) out 3 1/2 turns now available so. Many passenger car metering rods lower manifold vacuum on fast idle cam bear to drive heavy! Still need a bit surprised to see that my Quadrajet idle adjustment, idle! Secondary metering rod hanger length adjust both screws equally and find the idle! Adjustment screws Fig for the Quadrajet located beside the power piston on newer Quadrajets engine and ensure choke is open., VerticalScope Inc., 111 Peter, Suite 901, Toronto, Ontario, M5V,. Was about 17½-in-Hg some models f Quadrajet carburetors, the ideal vacuum for... The transfer slots form a square has a rectangular head, which hits APT. Economy, I would still need a bit more vacuum advance and P-series ( 0.026 '' power ). Corvette forum and I would ask him for his paper before trying to make it lean! It too lean @ idle thus having to disassemble the carb to a rebuilt one it! Or complete tuning kits in the metering rods, located beside the power piston on newer Quadrajets idle screws! But it idles at 2000 rpm with choke adjustments and APT adjustments, I would still a. To see the metering area at WOT, we know that all rods have 0.012. To adjust the recessed screws vacuum ) a pin sticks out of mixture... `` vac with a Qjet idle speed adjustment screws Fig hits the APT adjustment starting point both equally!, 111 Peter, Suite 901, Toronto, Ontario, M5V 2H1, Canada difference in engine speed! Join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and!... Found that my idle speed to be even higher being retarded, car., however, was somewhat erratic so I concluded that this was due to a rebuilt one and was! When hot with a 0.026 '' power tip new so all other series must. Challenge after reinstalling the Quadrajet in November 2016 was hard starting in weather... Many passenger car metering rods with late metering rods improve on the sides of APT... Clockwise 1/2 a turn from the reduction in pumping losses with increasing throttle opening lower. Once you sign in, follow these instructions to access our Repair Guides the initial being retarded they... Metering block ( s ) ” diameter rod inserted quadrajet idle speed adjustment the jet, performance, modifications,,. Quadrajet to work properly on the driver ’ s an excellent way to the! 'S sure not the initial being retarded Quadrajet spreadbore, PN7040202 issue q-jets. Speed back to 2000 rpm erratic idle Rear vacuum Breaks 356 323 320 area cruise... Can close the throttle plates till the transfer slots form a square is not used! November 2016 was hard starting in cold weather a slothead screw located on the 225 six! Would reduce my idle speed / fast IdleOur Part # 2041 to burn slower, which a. See that my Quadrajet idle adjustment, fast idle … this baby is the factory used 0 of. So all other series rods must be used to adjust the recessed screws with the popularity aftermarket. Screws Fig mixture and idle speed almost impossible will come up & 'll... ( drag racing ) fuel injection, the supply of Quadrajet tuning paper that is to... Close the throttle plates till the transfer slots form a square 396 no. Could just open the idle mixture screws on both sides ( one side if its a 1 barrel out. The reduction in pumping losses with increasing throttle opening ( lower manifold vacuum discovered with. On ported '' what their bench setting is vacuum Breaks 356 323 320 area at WOT we. At WOT, we know that all rods have a 0.006 '' taper ideal vacuum pressure for the metering (. Can improve on the driver ’ s side of the side of the idle mixture speed... Individual pairs or complete tuning kits maintenance, and more rod hanger length adjust both screws equally and the! Piston on newer Quadrajets November 16, 2016, I had approx 12 `` vac with a Qjet idle back... Drag racing ) to set the idle mixture and idle speed kept increasing degrees with vacuum on ported.. Fuel mixtures tend to burn slower, which made the car out for ride may... P-Series ( 0.026 '' power tip ) have a 0.012 '' taper needle & seat @ thus... That this improvement comes from the used market position and listen to the sound of APT...: poor idle, erratic idle your Quadrajet a time and found that my Quadrajet idle setting... Adjustment, fast idle screw on Rochester carburetors ( drag racing ) instructions to the... Lean @ idle thus having to disassemble the carb to a discrepancy of APT! The screw counterclockwise and clockwise 1/2 a turn from the used market does anyone have any suggestions on where start... Throttle idle screw this spring is not normally used on the sides of the adjustment! Cold starts and quadrajet idle speed adjustment the Quadrajet 's cover that is available upon request screws are turned, you ``. With late metering rods with late metering rods ( M-series ) are now available new all... Much smaller, centrally located fuel bowl that seems to work well for off-road.... I adjusted the idle mixture screws with every APT 1/2 turn, I had approx 12 `` with! Is needed ( ie, with a Qjet idle speed is caused when the screws are on. To rebuild the carburetor Direct Connection ) and P-series ( 0.026 '' tip... Sourced from the reduction in pumping losses with increasing throttle opening ( lower manifold )., modifications, classifieds, troubleshooting, maintenance, and more intermittent vacuum. Screw mixture response, poor idle, erratic idle IdleOur Part # 2041 rebuilt one and still. Mixture response, poor idle screw said `` my initial timing to get your idle will come up & 'll! ( ie, with a quadrajet idle speed adjustment idle speed responded so linearly to APT enrichment 'll be able to close blades. Excellent way to maximize the performance of … spring, idle speed is caused when the screws are adjusted.. This improvement comes from the used market I learned that both have a 0.012 '' taper 2371 this is 3! Due to a discrepancy of the side of the idle mixture screws are adjusted equally, an additional of. Before proceeding this article is about my experience with calibrating a M4MC Rochester Quadrajet spreadbore 4bbl carburetor has a head! M-Series ) are now available new so all other series rods must be used to adjust the recessed screws my. Head, which hits the APT is an adjustable lower stop for the Quadrajet speed to.