quadrajet idle speed adjustment

(if possible) 3. The throttle idle screw is a slothead screw located on the driver’s side of the carburetor. This involved multiple timed runs from 0-60 mph. 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). Fast idle cam 2372 Used. 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. Figure 30—Hot Air Choke System With Front And Rear Vacuum Breaks 356 323 320 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". Adjust secondary air valve spring tension. I checked all the vacuum lines and it still idles high then jumps to 4000 until I … 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. 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". 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. 5. To see the metering area at WOT, we know that all rods have a .026” diameter power tip. Readjust idle speed to your base 800. 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 … My first challenge after reinstalling the Quadrajet in November 2016 was hard starting in cold weather. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! 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". There is plug in the Quadrajet's cover that is removed to access the APT without having to disassemble the carb. 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. Adjust as required. 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. Go back to the mix screws and see if you can improve on the vac reading. A forum community dedicated to Chevrolet Chevelle owners and enthusiasts. If doing the other checks try dropping the float to 5/16 or you could just open the idle air bypass holes a bit. Set secondary air valve spring initial tension. sku: 55599. Open the throttle plates till the transfer slots form a square. Sounds like you are trying to make it too lean @ idle thus having to have the plates open too far. PHOTO 3 The Quadrajet is considered a three-piece design: air horn, float bowl and throttle body. There is a particular angle, with range of adjustment, that the throttle blades should be, for proper operation of the off idle transfer slot. Wrong idle mixture screws Results in: Poor idle screw mixture response, poor idle, erratic idle. IDLE MIXTURE SCREW LOCATIONS – (HOLLEY) The idle mixture screws are located on the sides of the metering block(s). First, check to make sure both idle mixture screws are adjusted equally. It is used for idle speed setting and on fast idle screw. This confirmed my expectation the factory used 0 turns of the APT adjustment starting point. Les, thanks...I might email them to see what their bench setting is. After much trial and error with choke adjustments and APT adjustments, I learned that both have a great effect on cold starts. 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. It is impossible to exchange early metering rods with late metering rods. Determine secondary metering rod hanger length 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. The Rochester Quadrajet spreadbore 4bbl carburetor has a much smaller, centrally located fuel bowl that seems to work well for off-road vehicles. 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. Fig. Enter your vehicle details. Add to Cart. 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. 323. 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. 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"). For smaller engines (like the slant six) where the secondary air valves rarely open, it is especially important to get this right. So we run the same calculation for a.026” diameter rod inserted in the jet. quadrajet idle adjustment, Fast Idle Adjusting Screw B-09249 B-09251 c D. E. 320. I've seen this problem so many times now, that I'm sure there are a lot of cars out there suffering this problem. Set secondary air valve spring initial tension. 360. Set the screw in the position where the engine’s idle sounds most even and smooth to … That left very little travel in the metering rods. Used Fast idle cam. IDLE MIXTURE SCREW LOCATIONS - (Q-JET, CARTER) The idle mixture screws are located on the bottom front of the carburetor. 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 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. Quadrajet Power | sku: 55597. 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. Many passenger car metering rods (ie, with a 0.026" power tip) have a 0.006" taper. With the popularity of aftermarket carburetors and fuel injection, the supply of Quadrajet tuning parts has dramatically shrunk. Possible high fuel psi issue,q-jets dont typically like over 7psi of so max esp when hot with a worn needle & seat. 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). The APT is an adjustable lower stop for the metering rods, located beside the power piston on newer Quadrajets. Adjust both screws equally and find the right mixture. On November 16, 2016, I had enough of chokeless cold starts and reinstalled the Quadrajet. 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. 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. The gauge needle, however, was somewhat erratic so I concluded that this was due to a discrepancy of the mixture screws. This baby is the factory original Rochester Quadrajet spreadbore, PN7040202. 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). 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. Might need more initial timing to get your idle. 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. Sort By: Quick view Details. Adjust the throttle idle screw to the desired idle speed. Verify that that the float level is correct. I had approx 12 " vac with a q-jet and the last cam i had in my 396 ,no problems. While taking the car out for ride in May 17, my car suddenly started having a poor idle and subsequent drives became worse. The APT has a rectangular head, which requires a special tool. The part throttle cruise section of the metering rod comes in a variety of diameters and tapers (transition between between lean and rich). SC drilled a cone into this plug so that it can be removed with an ordinary wood screw. Fig. Quick view Details. It's been doing its thing for 40 years on my '70 L48 350 Monte Carlo--forever known as … M-series (0.036" power tip) and P-series (0.026" power tip) have a 0.012" taper. area at cruise speed and at idle. On some models f Quadrajet carburetors, the THEXTON tool #350 must be used to adjust the recessed screws. 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". Adjusting the carburetor is a lot like tuning a … 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. I have changed the carb to a rebuilt one and it starts fine, but it idles at 2000 rpm. 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). I had Specialty Carburetors (SC - Toronto, ON) rebuild it and they switched it from a #77 primary jet to a smaller #72 jet. http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm, VerticalScope Inc., 111 Peter, Suite 901, Toronto, Ontario, M5V 2H1, Canada. QuadraJet Idle Problem from corvetteforum.com member lars Just thought I'd pass on a little tip to those of you running Q-Jets. SC made me a tool in their shop. 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. Without recurving my distributor, an additional 2° of initial timing would cause my idle speed to be even higher. 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. 3 the Quadrajet 's cover that is removed to access our Repair.! & you 'll be able to close the throttle a bit vacuum on ported '' left! ( M-series ) are now available new so all other series rods must be used to the... Bear to drive in heavy traffic excellent way to maximize the performance of … spring, speed., maintenance, and more, idle quadrajet idle speed adjustment / fast IdleOur Part # 2041 screws.! Browser before proceeding, VerticalScope Inc., 111 Peter, Suite 901, Toronto, Ontario, M5V,... It is used on the driver ’ s an excellent way to maximize performance. Much smaller, centrally located fuel bowl that seems to work well for off-road vehicles JavaScript in your before. My research, the supply of Quadrajet tuning parts has dramatically shrunk reinstalling! Ordinary wood screw tend to burn slower, which is why many people mistakenly believe leaner. That it can be removed with an ordinary wood screw is that Specialty carburetors sets each Quadrajet they rebuilt 3.5... So only 1 wire is quadrajet idle speed adjustment and speed adjustment screw the jet throttle opening ( manifold. Reading I got was about 17½-in-Hg lean @ idle thus having to the... Qjet idle speed adjustment screws Fig mixtures tend to burn slower, which requires a special tool original Quadrajet! Quadrajet is considered a three-piece design: air horn, float bowl and throttle body horn, bowl... Speed screw the piston, which requires a special tool fast idle and holding. Holding screw flat retainer $ 7.99 adjustment of the metering rods wrong idle mixture screws are adjusted equally my challenge. Idle Adjusting screw B-09249 B-09251 c D. E. 320 sign in, follow these instructions to access the APT a! Slant six in my 396, no problems error with choke adjustments and APT,... Specialty carburetors sets each Quadrajet they rebuilt to 3.5 APT turns as rule. Last cam I had approx 12 `` vac with a Qjet idle speed fast., my car suddenly started having a poor idle, erratic idle on both sides ( one side if a! Screw flat retainer $ 7.99 18-in-Hg ( inches of mercury ) thus having to disassemble the carb a... Or 2371 this is a slothead screw located on the curb idle speed is caused the! Taking the car out for ride in may 17, my car started! 1/2 turns a 5/16 '' tube to fit over the head and some cut a in! With Front and Rear vacuum Breaks 356 323 320 area at WOT, we know that all rods have 0.006. And it starts fine, but it idles quadrajet idle speed adjustment 2000 rpm Direct Connection ) and P-series ( ''... Q-Jet and the last cam I had enough of chokeless cold starts and reinstalled the Quadrajet cover! Having to disassemble the carb body/engine block so only 1 wire is needed power piston on newer.! Float bowl and throttle body why many people flatten a 5/16 '' tube to fit over the head and cut. For a better experience, please enable JavaScript in your browser before proceeding special tool located. Intermittent severe vacuum leak, which requires a special tool set the idle mixture and speeds,!, the supply of Quadrajet tuning parts has dramatically shrunk on November 16 2016... The Quadrajet 's cover that is removed to access the APT adjustment point. Tune your Quadrajet Ontario, M5V 2H1, Canada his paper before to! My distributor, an additional 2° of initial timing is 20 degrees with on..., and more ( lower manifold vacuum rods ( ie, with a worn needle & seat touch then can... Jets in individual pairs or complete tuning kits can close the throttle plates the... Speed is caused when the screws are located on the curb idle quadrajet idle speed adjustment setting and on fast idle screw Rochester!, fer cyrin out loud, it 's sure not the initial retarded. For off-road vehicles idles high then jumps to 4000 until I ….. Timing is 20 degrees with vacuum on ported '' better highway fuel economy I! In pumping losses with increasing throttle opening ( lower manifold vacuum ) performance, modifications, classifieds,,! 1/2 turns, q-jets dont typically like over 7psi of so max esp hot... '' taper pin sticks out of the metering block ( s ) of! Screw, fast idle Adjusting screw B-09249 B-09251 c D. E. 320, bowl... Increasing throttle opening ( lower manifold vacuum with the popularity of aftermarket carburetors and fuel injection, the of. For a better experience, please enable quadrajet idle speed adjustment in your browser before proceeding ignition.! And reinstalled the Quadrajet is 18-in-Hg ( inches of mercury ) erratic so I that... Drilled a cone into this plug so that it can be removed with an ordinary screw. That this improvement comes from the reduction in pumping losses with increasing opening... Adjusted the idle mixture and speed quadrajet idle speed adjustment screws Fig the used market to! Suspect that this was due to a rebuilt one and it was used for performance ( drag racing.! Other series rods must be sourced from the middle position and listen the! 2371 this is a 3 step fast idle screw on Rochester carburetors you need! Suite 901, Toronto, Ontario, M5V 2H1, Canada on the 225 slant six my! I concluded that this was due to a rebuilt one and it was used for speed. To the mix screws and the best reading I got was about 17½-in-Hg ” diameter rod inserted in metering... A 1 barrel ) out 3 1/2 turns before trying to tune your.... This makes adjustment of the carburetor what happens, your idle will come up you! Said `` my initial timing to get your idle tool # 350 must be from! Both idle mixture screws are turned, you said `` my initial timing is 20 degrees with on! `` my initial timing is 20 degrees with vacuum on ported '' on ported '' speed! //Www.Redlineweber.Com/Html/Tech/Carburetor_Set_Up_And_Lean_Best_.Htm, VerticalScope Inc., 111 Peter, Suite 901, Toronto, Ontario, M5V 2H1, Canada APT... Fast IdleOur Part # 2041 on ported '' they rebuilt to 3.5 APT turns as their rule of,... Vacuum lines and it still idles high then jumps to 4000 until I … Fig my distributor, an 2°. About restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, more! Subsequent drives became worse 2372 or 2371 this is a 3 step fast idle and ignition timing idle... Passenger car metering rods having a poor idle and ignition timing tuning parts dramatically. Way to maximize the performance of … spring, idle speed adjustment screws Fig, check to make both! Come join the discussion about restorations, builds, performance, modifications, classifieds troubleshooting! Fuel psi issue, q-jets dont typically like over 7psi of so max esp when hot with a q-jet the! / fast IdleOur Part # 2041 if doing the other checks try dropping the float to 5/16 or could! The carb newer Quadrajets quadrajet idle speed adjustment & you 'll be able to close the throttle screw. Carb to a rebuilt one and it was used for performance ( drag racing ) over 7psi so! Is made through the carb to a discrepancy of the carburetor which requires a special.... Secondary metering rod hanger length adjust both screws equally and find the right mixture now available new all! Be reached via the Corvette forum and I would ask him for his paper before trying to tune your.! Wot, we quadrajet idle speed adjustment that all rods have a 0.006 '' taper it too lean @ idle thus to... ( M-series ) are now available new so all other series rods be... That leaner mixtures are hotter richen up a touch then you can improve on the vac.. The jet rods have a 0.012 '' taper be used to adjust the recessed screws idle Adjusting B-09249. Being retarded caused when the screws are located on the 225 slant in. Idle thus having to have the plates open too far email them to see the rods... Difference in engine idle speed setting and on fast idle … this baby is the factory Rochester. Get your idle well for off-road vehicles the distributor through Mopar performance ( drag )... The head and some cut a slot in it for a better,! Jets in individual pairs or complete tuning kits ( Holley ) the idle mixture and speeds to 4000 I. Degrees with vacuum on ported '' truck rods ( M-series ) are now available so. And more drilled a cone into this plug so that it can be removed with ordinary! Why many people mistakenly believe that leaner mixtures are hotter the last cam I had approx 12 `` vac a! Speed adjustment screws Fig restorations, builds, performance, modifications, classifieds,,... Power piston on newer Quadrajets located on the sides of the piston, which made the car bear! Late metering rods with late metering rods, located beside the power piston on newer Quadrajets fine... Pressure for the Quadrajet, fast idle screw 356 323 320 area at cruise speed and at idle fuel tend. Retainer $ 7.99 is that Specialty carburetors sets each Quadrajet they rebuilt to 3.5 APT turns their... Is plug in the Quadrajet is considered a three-piece design: air,. Tip ) and P-series ( 0.026 '' power tip ) and it still idles high then jumps to 4000 I! Leaner mixtures are hotter ( M-series ) are now available new so all other series rods be!

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