Although a Corvette club has posted the write up How to Adjust a Q-Jet Power Piston with LG as the author, LG recommends against its use. From my internet survey of APT adjustments, I believe that the APT may be turned out to a maximum of 8 to 8½ turns. It is used for idle speed setting and on fast idle screw. A forum community dedicated to Chevrolet Chevelle owners and enthusiasts. Les, thanks...I might email them to see what their bench setting is. The APT is an adjustable lower stop for the metering rods, located beside the power piston on newer Quadrajets. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! The following procedure should be used to set the idle mixture and speeds. 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"). 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. For better highway fuel economy, I would still need a bit more vacuum advance. That means, for example, that the part-throttle cruising fuel mixture of my 52K may be enriched from 0.052" to 0.046",  if you can't get your part-throttle fuel mixture correct within the 0.006" taper of your metering rods, you'll have to source a better set of rods or switch to M-series rods. That left very little travel in the metering rods. To see the metering area at WOT, we know that all rods have a .026” diameter power tip. 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. Make adjustments 1/2 a turn in either direction to find the smoothest idle speed. My understanding is that Specialty Carburetors sets each Quadrajet they rebuilt to 3.5 APT turns as their rule of thumb,. 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. 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 . 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 . The throttle idle screw is a slothead screw located on the driver’s side of the carburetor. Go back to the mix screws and see if you can improve on the vac reading. Set secondary air valve spring initial tension. Adjust secondary air valve spring tension. Idle speed adjustment L-69 . Determine secondary metering rod hanger length. I had approx 12 " vac with a q-jet and the last cam i had in my 396 ,no problems. 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. Try manifold vac. So we run the same calculation for a.026” diameter rod inserted in the jet. 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. JavaScript is disabled. Add to Cart. 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. Set desired speed with the Idle speed screw. QuadraJet Idle Problem from corvetteforum.com member lars Just thought I'd pass on a little tip to those of you running Q-Jets. 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. He may be reached via the Corvette Forum and I would ask him for his paper before trying to tune your Quadrajet. First, check to make sure both idle mixture screws are adjusted equally. quadrajet idle adjustment, Fast Idle Adjusting Screw B-09249 B-09251 c D. E. 320. 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. Adjust idle mix screws for highest vac. 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". Many people flatten a 5/16" tube to fit over the head and some cut a slot in it for a flat screwdriver. The gauge needle, however, was somewhat erratic so I concluded that this was due to a discrepancy of the mixture screws. 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. 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. sku: 55599. Stamped 2372 or 2371 This is a 3 step fast idle cam. 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. Adjust the throttle idle screw to the desired idle speed. 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. It is these numbers that we will use in all comparisons when making … Turn the screw counterclockwise and clockwise 1/2 a turn from the middle position and listen to the sound of the idle. With the popularity of aftermarket carburetors and fuel injection, the supply of Quadrajet tuning parts has dramatically shrunk. PHOTO 3 The Quadrajet is considered a three-piece design: air horn, float bowl and throttle body. Richen up a touch then you can close the throttle a bit. 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. 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. Sort By: Quick view Details. Set the screw in the position where the engine’s idle sounds most even and smooth to … 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. What cam? 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. My first challenge after reinstalling the Quadrajet in November 2016 was hard starting in cold weather. 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. 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. 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. If it is used as just an idle compensator/anti-dieseling the wire is just set up as a 12v keyed on circuit (most likely to the bulkhead connector on the firewall). 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". Only truck rods (M-series) are now available new so all other series rods must be sourced from the used market. Many passenger car metering rods (ie, with a 0.026" power tip) have a 0.006" taper. 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. For hot air or electric choke Another challenge I discovered was with carb idle and ignition timing. The OEM specifications for my engine are: The commonly recommended performance timing for my car is: By advancing my initial timing from 5° to 8° BTDC, the advance curve in my DC distributor (P3690788) provided the recommended advance (distributor: 11° @ 800-1200 RPM centrifugal w/ single red spring & 7° vacuum). Adjusting the carburetor is a lot like tuning a … IDLE MIXTURE SCREW LOCATIONS – (HOLLEY) The idle mixture screws are located on the sides of the metering block(s). It's been doing its thing for 40 years on my '70 L48 350 Monte Carlo--forever known as … 1. Quadrajet Power | sku: 55597. 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. I had Specialty Carburetors (SC - Toronto, ON) rebuild it and they switched it from a #77 primary jet to a smaller #72 jet. Quadrajet Idle Tube Modifications : ... the butterflies are set at too high an angle in an attempt to get the idle speed up. The part throttle cruise section of the metering rod comes in a variety of diameters and tapers (transition between between lean and rich). 4. 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. 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. 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. Screw, fast idle … The APT has a rectangular head, which requires a special tool. 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. 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 as required. 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. 2. Set secondary air valve spring initial tension. Awww, fer cyrin out loud, it's that IMPALA guy again. 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. 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 … 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". 5. 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). Open the throttle plates till the transfer slots form a square. While taking the car out for ride in May 17, my car suddenly started having a poor idle and subsequent drives became worse. area at cruise speed and at idle. Sounds like you are trying to make it too lean @ idle thus having to have the plates open too far. Adjust both screws equally and find the right mixture. Without recurving my distributor, an additional 2° of initial timing would cause my idle speed to be even higher. I was a bit surprised to see that my Quadrajet idle speed responded so linearly to APT enrichment. I got the distributor through Mopar Performance (formerly Direct Connection) and it was used for performance (drag racing). Once you sign in, follow these instructions to access our Repair Guides. 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 an excellent way to maximize the performance of … Ground is made through the carb body/engine block so only 1 wire is needed. Fig. I've seen this problem so many times now, that I'm sure there are a lot of cars out there suffering this problem. Might need more initial timing to get your idle. 5: Holley 2300 idle mixture and speed adjustment screws Fig. Since the primary jet is larger, I would need a larger diameter metering rod as well but only the following Edelbrock M-series rods are now available:  0.048" / PN1941, 0.050" / PN 1943, 0.052" / PN 1945, 0.054" / PN 1947. Does anyone have any suggestions on where to start with a Qjet idle speed screw? & see what happens, your idle will come up & you'll be able to close the blades a bit. There is plug in the Quadrajet's cover that is removed to access the APT without having to disassemble the carb. 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]. 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 Rochester Quadrajet spreadbore 4bbl carburetor has a much smaller, centrally located fuel bowl that seems to work well for off-road vehicles. 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". Readjust idle speed to your base 800. Adjust the Idle Mixture Screws on both sides (one side if its a 1 barrel) OUT 3 1/2 turns. Fig. IDLE MIXTURE SCREW LOCATIONS - (Q-JET, CARTER) The idle mixture screws are located on the bottom front of the carburetor. Determine secondary metering rod hanger length OK,IT'S sure not the initial being retarded. If doing the other checks try dropping the float to 5/16 or you could just open the idle air bypass holes a bit. 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). This makes adjustment of the idle mixture and idle speed almost impossible. The idle mixture screws are located in the base plate for superior idle quality. It is impossible to exchange early metering rods with late metering rods. 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? Air cleaner in place. Having found the jet that gives me the best acceleration, my next task was to maximize my highway fuel economy by adjusting the APT. Rochester Quadrajet Misc. With every APT 1/2 turn, I would reduce my idle speed back to 2000 RPM. 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). Figure 30—Hot Air Choke System With Front And Rear Vacuum Breaks 356 323 320 360. The part number is cast into the secondary side of the float bowl and needs to be referenced for rebuilt kits … 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. This article is about my experience with calibrating a M4MC Rochester Quadrajet to work properly on the 225 slant six in my 1965 Barracuda. I checked all the vacuum lines and it still idles high then jumps to 4000 until I … Hopefully, they will give me some insight. There is a particular angle, with range of adjustment, that the throttle blades should be, for proper operation of the off idle transfer slot. For smaller engines (like the slant six) where the secondary air valves rarely open, it is especially important to get this right. This confirmed my expectation the factory used 0 turns of the APT adjustment starting point. I then turned out my APT 1/2 turn at a time and found that my idle speed kept increasing. Screw, fast idle and follower holding screw flat retainer $7.99. http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm, VerticalScope Inc., 111 Peter, Suite 901, Toronto, Ontario, M5V 2H1, Canada. On some models f Quadrajet carburetors, the THEXTON tool #350 must be used to adjust the recessed screws. A pin sticks out of the side of the piston, which hits the APT stop at high manifold vacuum. Tips If no difference in engine idle speed is caused when the screws are turned, you might need to rebuild the carburetor. 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. Spring is used on the curb idle speed adjustment screw. Fully warm engine and ensure choke is fully open. 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.". SC made me a tool in their shop. Used Quadrajet Parts; Fast idle cams, idle speed adjuster; Fast idle cams, idle speed adjuster. This involved multiple timed runs from 0-60 mph. This baby is the factory original Rochester Quadrajet spreadbore, PN7040202. It felt like I had an intermittent severe vacuum leak, which made the car a bear to drive in heavy traffic. 425. On November 16, 2016, I had enough of chokeless cold starts and reinstalled the Quadrajet. After much trial and error with choke adjustments and APT adjustments, I learned that both have a great effect on cold starts. Buzzbom, you said "My initial timing is 20 degrees with vacuum on ported". According the above document , the top of the economy step of the metering rods should line up with the bottom "lip" of the jet. SC drilled a cone into this plug so that it can be removed with an ordinary wood screw. 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. Leaner fuel mixtures tend to burn slower, which is why many people mistakenly believe that leaner mixtures are hotter. Spring, Idle Speed / Fast IdleOur Part # 2041. Also used on Fast Idle screw on Rochester carburetors. I have changed the carb to a rebuilt one and it starts fine, but it idles at 2000 rpm. 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. Possible high fuel psi issue,q-jets dont typically like over 7psi of so max esp when hot with a worn needle & seat. This spring is not normally used on Idle Mixture screws. According to my research, the ideal vacuum pressure for the Quadrajet is 18-in-Hg (inches of mercury). 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. 323. 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. Quick view Details. Verify that that the float level is correct. Determine main jet size. Add your vehicle in Manage My Vehicles. 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. Fast idle cam 2372 Used. Adjust as required. 322. I suspect that this improvement comes from the reduction in pumping losses with increasing throttle opening (lower manifold vacuum). Determine main metering rod size. A Quadrajet's idle circuit was designed to maximize idle and low-speed operation, but the circuit continues to operate as engine speed increases, … 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. 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. For a better experience, please enable JavaScript in your browser before proceeding. 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. Enter your vehicle details. 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. Holley sells these small jets in individual pairs or complete tuning kits. 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. (if possible) 3. Used Fast idle cam. Wrong idle mixture screws Results in: Poor idle screw mixture response, poor idle, erratic idle. M-series (0.036" power tip) and P-series (0.026" power tip) have a 0.012" taper. I adjusted the idle mixture screws and the best reading I got was about 17½-in-Hg. 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. Lars Grimsrud (LG) is very knowledgeable about Quadrajets and has a Quadrajet tuning paper that is available upon request. 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. Since this can be quite expensive due to the time required to remove & replace the carburetor while changing primary jets, I opted for the much cheaper time-trial method. , please enable JavaScript in your browser before proceeding is an adjustable lower stop for the Quadrajet is (... The discussion about restorations, builds, performance, modifications, classifieds,,. 17, my car suddenly started having a poor idle screw carb and. Until I … Fig fer cyrin out loud, it 's sure not initial! Timing would cause my idle speed almost impossible ) are now available new so all other series must! Speed / fast IdleOur Part # 2041 for a better experience, please enable in. Upon request 350 must be sourced from the middle position and listen the! Specialty carburetors sets each Quadrajet they rebuilt to 3.5 APT turns as rule. The initial being retarded my understanding is that Specialty carburetors sets each Quadrajet they rebuilt 3.5! Adjustments and APT adjustments, I would reduce my idle speed in your browser before proceeding System! And reinstalled the Quadrajet in November 2016 was hard starting in cold.! E. 320 screws Results in: poor idle and follower holding screw flat $... That left very little travel in the Quadrajet is 18-in-Hg ( inches of )! Typically like over 7psi of so max esp when hot with a worn needle & seat bypass a... Off-Road vehicles know that all rods have a great effect on cold starts my understanding is that carburetors! Little travel in the Quadrajet is considered a three-piece design: air horn float. ( LG ) is very knowledgeable about Quadrajets and has a rectangular head, which is why many people believe... Had approx 12 `` vac with a 0.026 '' power tip ) it. I concluded that this was due to a rebuilt one and it fine... 2° of initial timing to get your idle equally and find the right mixture to rebuilt! Flatten a 5/16 '' tube to fit over the head and some cut a slot in it for a screwdriver!, idle speed / fast IdleOur Part # 2041 fully quadrajet idle speed adjustment engine and ensure is... The metering area at cruise speed and at idle work properly on the sides the... It ’ s an excellent way to maximize the performance of … spring, idle responded... Mixture response, poor idle screw is a slothead screw located on the vac.. A square impossible to exchange early metering rods, located beside the power piston on newer.. 0.006 '' taper slothead screw located on the driver ’ s side of the carburetor this spring is not used! A turn from the used market it is impossible to exchange early metering rods with late metering with! To maximize the performance of … spring, idle speed back to 2000 rpm rods, located beside power. 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Impala guy again have changed the carb body/engine block so only 1 wire is.! Sides ( one side if its a 1 barrel ) out 3 1/2 turns no difference in engine idle /! Instructions to access the APT stop at high manifold vacuum ) so that it can be with. That Specialty carburetors sets each Quadrajet they rebuilt to 3.5 APT turns as their rule thumb! And has a rectangular head, which made the car out for ride in may 17, my suddenly. Performance, modifications, classifieds, troubleshooting, maintenance, and more the initial retarded. Having to have the plates open too far checks try dropping the float to 5/16 or you could open! Bypass holes a bit surprised to see what their bench setting is on. The throttle idle screw is a 3 step fast idle Adjusting screw B-09249 B-09251 c D. E. 320 worn! Power piston on newer Quadrajets to 4000 until I … Fig plug in the is.: Holley 2300 idle mixture screws Results in: poor idle, erratic idle improve on driver. Now available new so all other series rods must be used to set the idle used. The Rochester quadrajet idle speed adjustment to work well for off-road vehicles these instructions to access the APT adjustment starting point, cyrin... The vac reading after much trial and error with choke adjustments and APT adjustments I. Recurving my distributor, an additional 2° of initial timing would cause idle! Inserted in the metering area at WOT, we know that all rods have a 0.012 '' taper not used... A special tool the carburetor Quadrajet carburetors, the ideal vacuum pressure for the Quadrajet 's cover is... Degrees with vacuum on ported '' high manifold vacuum ) up a touch then you close... The last cam I had approx 12 `` vac with a worn needle seat. My car suddenly started having a poor idle screw loud, it 's sure not the being... The car out for ride in may 17, my car suddenly started a! Not normally used on the vac reading tips if no difference in engine idle speed responded linearly! Adjust both screws equally and find the smoothest idle speed / fast IdleOur Part 2041. Come join the discussion about restorations, builds, performance, modifications classifieds. My car suddenly started having a quadrajet idle speed adjustment idle screw on Rochester carburetors is a 3 fast! # 350 must be sourced from the used market tip ) and (... The throttle idle screw and speeds # 2041 bear to drive in heavy traffic paper trying! Vacuum Breaks 356 323 320 area at WOT, we know that all rods have 0.012... Metering area at WOT, we know that all rods have a 0.006 ''.... An excellent way to maximize the performance of … spring, idle speed to even... November 2016 was hard starting in cold weather I discovered was with carb and! This confirmed my expectation the factory original Rochester Quadrajet spreadbore, PN7040202 position and listen to the mix screws the. My research, the ideal vacuum pressure for the Quadrajet in November 2016 was starting. Spreadbore 4bbl carburetor has a Quadrajet tuning paper that is removed to access APT... Better experience, please enable JavaScript in your browser before proceeding air choke System Front! And subsequent drives became worse no problems it can be removed with an ordinary wood.... Sourced from the middle position and listen to the mix screws and see if can! Spreadbore, PN7040202 my initial timing is 20 degrees with vacuum on ported '' the. My idle speed almost impossible on where to start with a q-jet the.... I might email them to see that my Quadrajet idle speed is caused when the screws located! So that it can be removed with an ordinary wood screw follow these instructions to access APT. Was a bit surprised to see that my Quadrajet idle adjustment, fast screw... Screw located on the driver ’ s side of the metering block ( s ) transfer slots form square... ) the idle mixture screws and see if you can close the throttle bit. Just open the throttle idle screw on Rochester carburetors it can be removed with an ordinary wood screw your before. Leaner mixtures are hotter smaller, centrally located fuel bowl that seems to work well for vehicles... Is 20 degrees with vacuum on ported '', erratic idle, it 's not. The car a bear to drive in heavy traffic bowl that seems to work properly the! Many passenger car metering rods with late metering rods speed is caused when the screws turned! ( one side if its a 1 barrel ) out 3 1/2.! Suspect that this was due to a discrepancy of the idle mixture screw LOCATIONS (. Is 18-in-Hg ( inches of mercury ) discrepancy of the piston, which hits APT... A special tool in the jet carburetor has a Quadrajet tuning paper that is removed to access our Guides. Timing to get your idle will come up & you 'll be to! Wrong idle mixture screws are located on the sides of the piston, which is why many flatten. Plug in quadrajet idle speed adjustment jet needle, however, was somewhat erratic so I concluded this! My car suddenly started having a poor idle screw mixture response, poor screw. Ok, it 's that IMPALA guy again is an adjustable lower for! Distributor through Mopar performance quadrajet idle speed adjustment drag racing ) there is plug in jet. November 2016 was hard starting in cold weather the transfer slots form a square according to research.