The following is a chart of potential carburetor problems and possible remedies. It's not the choke, it's working fine, and it will still flood on cold start if I deactivate the choke. This is an easy one. JEGS is the source for performance parts with Same Day Shipping. As Shaun asked is the vacuum advance working. in my opinion, because when the car is warmed up she runs fantastic. Fuel pressure should not drop below 2. This ones got me scratching my head and it's probably something obvious. The vacuum at idle peaks at 18, when bot. The idle screws on a Rochester Quadrajet carburetor fine tune the air-fuel ratio going into the engine during idle. See our Performance Carburetors, Intake Manifolds, Cylinder Heads, Crate Engines, Electronic Fuel Injection. The computer is the brains of a computerized engine control system and sensors are its link to what’s happening under the hood. Pair of replacement Quadrajet screws, fi. Coast Guard's stringent specifications. What the idle mixture screw does NOT do. The metering rods are not designed to limit fuel at idle, they are for part throttle cruise fuel economy. Turn screws adjusting both idle and main mixture in (clockwise) finger tight, however over tightening the screws may partially or entirely damage the tapered portion of the needle. NOTE: Edelbrock Performer Series carburetors are not for computer-controlled applications. The caps can be removed. 1987 RC 360 Carburetor problems- Choke. They seem to do nothing. On the Monojets that use the electronic solenoid, disconnect the solenoid, then adjust the idle using the solenoid. The idle mixture screws are located in the base plate for superior idle quality. It's not precise, but it doesn't need to be. Uses a common 3/16" hex socket. In the old days it used to go that a rich fuel mixture will make the plug go black and a lean one would make it go a chalky white color, optimum burning will make your plugs go brown. Carburetor Mixture Screws Carbs Unlimited has Rebuild Parts and Restoration Parts for All Types of Carburetors, including rebuild kits, floats, pulloffs, and chokes. Put a sheet in the box with your name, contact info, email, and description of your vehicle, and engine specs, especially cam and compression if known. Reason, the "boob's" who rebuilt the carb many years back for me, enlarged the primary jets. Runs good and eliminated any bogging, but I want to get more performance out of it. Typically if everything is right 3 to 3 and 1/2 turns out is correct with Carter and Rochester carburetors. Buy A-Team Performance 1903R - Remanufactured Rochester Quadrajet Carburetor 750 CFM 4MV Compatible with GM Chevy Chevrolet 1975-1985 Hot Air Style Choke Carb: Carburetors - Amazon. A long screwdriver doesn’t meet the screw dead-on b/c of the. We're going to adjust the mixture screws so that they are metered correctly. With the engine up to operating temps, turn the screws in until the engine starts to stumble. Fuel pressure should not drop below 2. Thus, a change in the main metering circuit (jets and/or rods) will affect the idle circuit. If you did not add a measured amount, I would repeat that test using a measured amount in both primaries to see if you get the same result - one primary RPMs increase, the other primary RPMs decrease. If your car does not have the system hooked up properly, it could overheat on a hot day when you’re stuck in traffic, which could reduce the life of your engine. The Quadrajet looks pretty good back on the slant six. The butterfly should close freely when the engine is cold and the throttle is opened enough to release the fast-idle cam. If, you were going to climb higher in altitude and, stay there for quite a while, like say, a couple of weeks or more, then, it might be worth it for you to dismantle the carb and install to smaller main jets. The little valve in the paper filter is a roll over device that stops fuel flow in case of an accident. US manufactured and ethanol ready. This will help balance the idle mixture and allow the engine to run as. Contrary to popular belief, the idle mixture control screws DO NOT adjust the mixture. I’m working on an engine for Terry Slaton with a go street 400hp. Start the engine and let it warm to normal operating temperature. 2017 Tool Book pages 1104 - 1411. The idle mixture is o. If the accelerator pump wasn't working correctly, be sure to attach the linkage to the pump arm hole nearest the pivot to get the biggest pump shot. Turn back in (for lean idle adjustment) 1/4 turn. Then out until you get a smooth idle. Put a sheet in the box with your name, contact info, email, and description of your vehicle, and engine specs, especially cam and compression if known. The idle mixture control screws control the VOLUME of the preset mixture. Using an Edelbrock rebuild kit on a four-barrel Quadrajet after years of non-use to bring it back to life. The idle mixture screws are located in the base plate for superior idle quality. the initial idle mixture setting should be 1 1/2 turns out. Loosen the allen head screw until you see the tension go completely out of the butterfly. A long screwdriver doesn’t meet the screw dead-on b/c of the. The 2 best patent attornies in the world have stated so. New pair Quadrajet air idle mixture screws, early style. With the engine up to operating temps, turn the screws in until the engine starts to stumble. The developer states that this was accomplished "by replacing the PCV valve with one of larger capacity to lean put the mixture at cruise conditions and then ad- justing the idle mixture adjustment screws to lean best idle" (Reference 4). What the idle mixture screw does NOT do. Adjust the carburetor idle speed screw (NOT the solenoid plunger) to obtain 700 rpm (manual transmission in Neutral or automatic transmission in Drive). If the air/fuel mixture is too lean at idle or part throttle and the idle mixture screws do not provide enough adjustment, the correction may involve enlarging the idle jet. should be idling around 30. Seized/rusted idle mixture screws. Edelbrock carburetors are probably the easiest to work with on the market. #1409 & #1410 ONLY) IDLE MIXTURE SCREWS Left screw for left side of carb Right screw for right side of carb FUEL INLET for 3/8” hose (Except marine models #1409 & #1410 which use a 3/8” inverted flare fitting) CANISTER VAPOR VENT (#1400 Only. Remove any non-metal parts and soak mixture screws in carburetor cleaner for 15 minutes. Some carburetors have a slow speed fuel adjusting screw that regulates the fuel/air mixture in the lower rpm range. Bought a "new" winter car yesterday. At 3 it was almost willing to idle, at 4 it was better. Repeat the operation on 2 and 4V carburetors. When you turn them clockwise, you're leaning them out, so if you turned them counterclockwise, you fattened it up quite a bit. Not to keep asking same questions repeatedly , but with the air horn off and carb mounted , engine off , do you feel the float needles are seated ? Questioning my understanding of this design. The manual says idle is 1900 RPM +/- 100 rpm. Before drilling them bigger, I could turn the screws all the way in and not affect the idle. The jets and rods will make or break your off idle circuit and cruise range though. 26" overall length. Is this a two or four barrel carburetor and what make carb. Then leave sufficient time for the carburetor to respond and move to the next adjuster screw. Some of these had plastic caps to limit travel. but can increase engine wear by washing the lubricant from the Cylinder walls and diluting the crankcase Oil. 65:1 rocker arm to get that valve up and out of the way QUICKLY!. I wanted to ask those of you that have dealt with this a question before I proceed. I have a question regarding the idle mixture screws on my 600 cfm 4160 carb. Finally set the idle speed with the adjustement screw so it idled around 650 rpm in Park. Quadrajet 4 MC, 4 MV Carburetor Trouble Shooting E4MC, E4ME Adjustment Procedures I have a Rochester Quadrajet Marine Carburetor #17059286. Carburetor idle or mixture screws do not react Detailed Quadrajet Carburetor Rebuild COMPLETE GUIDE Toyota 4k Carburetor Idle speed & idle mixture adjustment English Subtitle. If you don't use that throttle blade setting, the transfer doesn't work right and hesitations abound. Using an Edelbrock rebuild kit on a four-barrel Quadrajet after years of non-use to bring it back to life. AED has combined every possible add-on feature and incorporated them into each kit to give you improved performance from your Holley Carburetor. Trash in the needle seat after a rebuild is not that unusual- I had this happen with my last rebuilt q-jet. It starts and idles nicely, the timing has been set, but the quadrajet still needs work. To start I set my idle speed at about 700rpm and turned one of the idle mixture screws in until the engine stumbled and then I turned it back 3/4 of a turn. 1987 RC 360 Carburetor problems- Choke. anything above idle and it starts pulling fuel from the idle transition slots. I repeated that with the other screw as well. The problem is, on the air cleaner it says, "Idle mixture screws are set from the factory and sealed" Because of this, I cannot seem to find these idle mixture screws. With crankcase blow-by gasses unable to escape, idle will. 7) Check idle cut-off solenoid, especially for. Those two mixture screws end up to be almost 1 turn each for me(just for a starting point for you). com by AUTOMOTION Rochester Carburetor Service. NOTE THAT THE CHOKE ITSELF MUST BE WORKING IN ORDER FOR THE FAST. ( a tach is best though, adjust for highest speed) After the the mixture screws are set adjust the idle screw. The Quadrajet uses a Double "D" carburetor adjusting tool. The Quadrajet's basic design didn't change much over its 25-year production life with the exception being the introduction of APT (Adjustable Part Throttle) in 1968 and electronic mixture. You're turning the idle mixture screws the wrong way. The engine should pick up speed and begin to smooth out. It's not precise, but it doesn't need to be. - posted in Engine: Ok Rusty the Torana is up and running but I have a small problem with the quadrajet. They started making Rochester Quadrajet 4 barrel carburetors in 1965. Adjust the idle to 800 or 900 rpm and set the idle mixtures screws for best/highest idle (highest vacuum). If the idle speed changes a little bit after it has been running, that is normal (open loop when first started vs. The only way I could get it to idle, was with both mixture screws fully closed (seated). Idle speed and mixture are controlled strictly by the computer emissions system. The Quadrajet uses a Double "D" carburetor adjusting tool. If the cruise mixture is off, first change the jets to get the A/F mixture correct at 2,500-3,000 rpm cruise range. Start the engine and let it warm to normal operating temperature. The first thing to do is not set up the idle speed, but to set the Idle mixture screw to lean best idle setting. I have been going through it trying to get ready for the strip on Friday. Now most of the fuel mixture the engine gets comes from the transition slots, not the idle mixture pinholes - so the idle mixture screws don't affect the idle mixture any more! Also these transition slots are designed to feed the engine at part throttle, not idle, so they will be way too rich at idle. When i put my hand over the top slightly starts to idle higher like it is sucking air from somewhere. Changes in the idle systems of these models make it impossible to properly adjust the mixture without the use of a propane enrichment system, not available to the general public. Cold, idle is rough and a little choppy, but once it is warm it usually runs smooth (except for when it dies) I have played around with the mixture screws and set them to max vacuum (around 15Hg) I have replaced the power valve multiple times just to be sure, but the screws still change how it runs every time. The mixture delivered by the carburetor is controlled by the idle tubes (gasoline jets), and the idle air bleeds (air jets) in the carburetor. The CFM rating is around 650 cfm. Thus, a change in the main metering circuit (jets and/or rods) will affect the idle circuit. If you did not count. The butterfly should close freely when the engine is cold and the throttle is opened enough to release the fast-idle cam. Therefore, the adjustment screws need not and should not be turned "in sync". Check it for interference. The developer states that this was accomplished "by replacing the PCV valve with one of larger capacity to lean put the mixture at cruise conditions and then ad- justing the idle mixture adjustment screws to lean best idle" (Reference 4). It is a good carburetor for fuel economy and still has stellar performance when required. Symptoms of a Bad or Failing Accelerator Pump a problem in the fuel mixture during acceleration. Address to: Quadrajet Power LLC. I've seen this problem so many times now, that I'm sure there are a lot of cars out there suffering this problem. After you start the car place the glass on the block where you can see it. The following is a chart of potential carburetor problems and possible remedies. example: 7028219 dg1938 quadrajet carburetor problems indexnewspaper. Adjust the idle mixture screws alter nately to obtain the maximum smooth idle speed. Not all carburetors are adjustable currently but older models are adjustable. The butterfly should close freely when the engine is cold and the throttle is opened enough to release the fast-idle cam. the timing should be 7 deg @1100 rpm. carburetor idle mixture screw seat; carburetor idle mixture screws tool; carburetor Honda 70 idle problem; carburetor maxture valve factory setting for Honda v6 150 motor; carburetor mixture screw adjusts what; carburetor mixture screw at the bottom or in the middle; carburetor mixture screw+speed screw+adjustment; carburetor on a 2001 Honda. By outside the envelope I mean the two idle mixture screws are out 3 to 4 turns instead of the average 2 to 3, and the timing has to be advanced. I have tried to make a study of quadrajet tuning. Curing Quadrajet Carb Woes--Here Are Some Interesting 21st Century Fixes For Your 20th Century Rochester Carburetor - Super Chevy Magazine. Since I have had my Holley 5200, I have been puzzled by the idle mixture screw setting. Just count the turns as you re-seat them so you'll know how far to. It has a 350 4bbl. Loosen the allen head screw until you see the tension go completely out of the butterfly. 1936 - change to 3 screws holding the airhorn eliminated breakage due to instability. Some other shop installed it but could not make it run correctly. Make one adjustment only to the first screw. 30 over, 6x-8 heads w/o porting, Comp XE274, 1. Thus, a change in the main metering circuit (jets and/or rods) will affect the idle circuit. com by AUTOMOTION Rochester Carburetor Service. i pulled the. US manufactured and ethanol ready. We are the premiere place for 1st gen and 2nd gen Dodges as well as a great source for newer models as well. Each has a special marine carburetor fuel-metering system calibrated specifically for the unique engine loads found on watercraft and J-style vent tubes to direct fuel and fumes back into the carburetor for safe operation in rough waters. JEGS is the source for performance parts with Same Day Shipping. Your cam is not that radical that it should need to idle that high. Nothing was right with the primaries. Q: Quadrajet Carb Problem. The vacuum at idle peaks at 18, when bot. So i think adding the extra fuel at idle via the mixture screws will solve my issues. That particular code should have the large A. The primary metering rod determines fuel mixture at cruise speed and determines responsiveness of the idle mixture screws and off-idle performance. An overly- rich mixture not only wastes fuel. Easily share your publications and get them in front of Issuu’s. There is a stumble or miss at idle, but once off idle it runs fine and has good power. Holley carburetors are notorious for loose idle-mixture screws that richen the idle mixture. the engine stalling when under load at idle not moving would not be distributor with the advance not working since at idle it should not be advanced. Or in, I use a baseline of 1 1/2 turns out from fully closed on the mixture screws. It starts and idles nicely, the timing has been set, but the quadrajet still needs work. Thread a 0-80 stainless screw into idle tube. Next, back them out 1 full turn and restart the engine making sure the choke is completely off. Seized/rusted idle mixture screws. I bought my car a month ago. -IF all checks out, set the base idle and then turn the idle mixture screws all the way in and come back out 3 COMPLETE turns on each one (many people confuse a 1/2 turn for a complete turn, if the screw is a flathead and you start straight up and down, the next time you come to straight up and down is only a 1/2 a turn) With the vaccum gauge. If the motor is having a serious stumble off-idle, does it do it under load only or any time the throttle goosed. I have ran into a problem that i cant seem to track down. The Quadrajet continued for the rest of the 1970s without any significant changes. I bought my car a month ago. carburetor idle mixture screw seat; carburetor idle mixture screws tool; carburetor johnson 70 idle problem; carburetor maxture valve factory setting for johnson v6 150 motor; carburetor mixture screw adjusts what; carburetor mixture screw at the bottom or in the middle; carburetor mixture screw+speed screw+adjustment; carburetor on a 2001. Do these regulate the air or the fuel going in. Then, start your car and let it warm up. When I dial them in all the way, I. And the idle mixture screws adjusted accordingly, as now they have an effect. The stock Quadrajet on my 1978 350 has no idle mixture adjustment screws! I didn't notice this until I'd already gone to the trouble of cleaning the carb, bolting it onto my new manifold, and adapting all my linkages, etc. Adjust the carburetor idle speed screw (NOT the solenoid plunger) to obtain 700 rpm (manual transmission in Neutral or automatic transmission in Drive). Unfortunately there is no data that can match the idle mixture screw to a specific carburetor number, so the idle screws are listed by size. What make vehicle is it ? Normally the idle mixture screws should be opened 1 and a half turns to two turns. The distributor and fuel filter are both in the way. i screw them both all the way in and the truck still starts and has high rpms please help me. Recommended by Edelbrock since 1994, we are a small specialized shop that provides Our Customers with ‘Custom’ Hot Rod Tri-Power Systems and Parts that are based on the versatile Rochester 2-Jet / 2GC Carburetor. Make one adjustment only to the first screw. Box 4797, Portland, OR 97208 or online at [email protected] Please keep an eye on the following areas during dis-assembly and rebuild. The stock Quadrajet on my 1978 350 has no idle mixture adjustment screws! I didn't notice this until I'd already gone to the trouble of cleaning the carb, bolting it onto my new manifold, and adapting all my linkages, etc. How to adjust Quadrajet/Dualjet key. First, turn in the mixture screw until the engine dies or runs worse, then back out the screw (recommend turning ¼ to ½ turn at a time). You're turning the idle mixture screws the wrong way. We're going to adjust the mixture screws so that they are metered correctly. At idle the throttle plates (160) are closed and very little air enters through the carb throats. when I saw open I mean a crack, but enough to cause the car to want to idle around 2500 rpm. Looking down the throat the throttle looks closed but have not ripped the carby off to check. Box 4797, Portland, OR 97208 or online at [email protected] I think we can figure out how things work from there. With a high mileage engine, that idle speed may not work. So i think adding the extra fuel at idle via the mixture screws will solve my issues. Internet wisdom indicated that a larger idle jet was needed however, the larger jet ran the off idle mixture too rich as measured by an O-2 sensor. Another indication could be when your carburetor is flooding. Following your advices increased holes behind ifle mixture screws to. The idle adjust screws probably are not the cause of the sooted plugs. Is there a trick to lean out a quadrajet at idle? I have the idle mixture screws both turned just about all the way in and it's still running rich. At IDLE, there should not be any more than 5. Now it still has a slight hesitation just off idle, but not to where it pops back thru carb. Re: quadrajet idle mixture screws all the way in Carefully check for vacuum leaks including the pcv valve and the base of the carb. " On a Q-Jet, we see that we can control the fuel mixture throughout the operating range. Some people think you're supposed to turn the idle mixture screws all the way in, and then back them out 2 1/2 turns. I am working on my fathers boat which has a 454 with a performer manifold and quadrajet carb. It was running super rich. Trash in the needle seat after a rebuild is not that unusual- I had this happen with my last rebuilt q-jet. These are not all my personal experiences but a lot can be gleened from this information. By outside the envelope I mean the two idle mixture screws are out 3 to 4 turns instead of the average 2 to 3, and the timing has to be advanced. The idle circuit consists of a non-adjustable fuel/air bypass that allows the carb to idle steadily without tipping into the primary circuit. It's very tight but if you unplug a small vacuum line located just in front of it you can get a torx fitting with a small ratchet on the adjustment screw and turn it. When trying to adjust the idle screws, The engine did not change until the screws were, almost all the way in, or many turns out. can be created when the accelerator pump is not working. If the motor is having a serious stumble off-idle, does it do it under load only or any time the throttle goosed. Since I have had my Holley 5200, I have been puzzled by the idle mixture screw setting. SERVICE BULLETIN 12-53 Page 1 of 4 The carburetor on these models have been factory preset to C. From1965-1979 Most will have 7/8 inch 20 fuel inlet till 1971 and 1 inch 20 after. #1409 & #1410 ONLY) IDLE MIXTURE SCREWS Left screw for left side of carb Right screw for right side of carb FUEL INLET for 3/8” hose (Except marine models #1409 & #1410 which use a 3/8” inverted flare fitting) CANISTER VAPOR VENT (#1400 Only. Once cleaned out, and the screws reinstalled to the recorded specs, if the idle is still unacceptable then with the aid of a vacuum gauge you can adjust them to get the smoothest idle. If the cruise mixture is off, first change the jets to get the A/F mixture correct at 2,500-3,000 rpm cruise range. If using a vacuum gauge as the writer above suggests, turn each screw independently for the highest vacuum. The other problem could be that you have the idle speed set high enough that the carb is no longer being controlled by the idle circuit. market, the last cars using carburetors were:. Most of these steep-taper screws are brass. Still at idle the A/F gauge reads 17 to pegged past 18 with the idle mixture screws probably close to. Motor is basically standard. Some ~77-79 contained internal restrictors to mixture adjustment. There are a pair of mixture screws, one located in front of each venturi on the base plate that allow the idle fuel/air ratio to be trimmed but overall adjustment is limited. The idle adjust screw is backed all the way out and the mixture screws are adjusted. This is an easy one. The screw adjustment (explained in the video) is used to fine tune this adjustment at idle speed only. Play up those low rpm qualities if you have one of the bigger displacement Pontiac engines by porting the cylinder heads and getting the valvetrain worked out so you can further exploit the low rpm benefits of the 455 by tailoring the valve events appropriately! Use a 1. It’s a very frustrating job b/c of the slotted screw head and their location. Mixture screws: the screws are readily accessible on 71-79 TQs. These carbs don't have an isolated idle circuit, so closing the idle mixture screws won't necessarily shut down the engine. The carburetor you pictured is a Rochester 4GC, not a Quadrajet. try 15 degrees advance at idle, then plug in the vacuum advance to the manifold vacuum for another 15. The hardware was not quite the correct length, so I reused some of the studs that were on the weber. This chart is intended to be a helpful guide when troubleshooting your carburetor. To adjust your idle speed, find the idle mixture screw that limits the flow of fuel at idle. port in the rear of the base plate. 7L VIN H 1-bbl (1983)) Dodge Workshop Manuals > Maintenance > Tune-up and Engine Performance Checks > Air/Fuel Mixture > System Information > Adjustments > Idle Mixture and Speed Adjustments > Page 332 Air/Fuel Mixture: Adjustments Idle Mixture (Propane Method) This procedure should only. Assuming everything else on the engine is OK, a rebuilt carb should allow the engine to run even if the mixture screws and idle screws are not set quite right. At idle the throttle plates (160) are closed and very little air enters through the carb throats. Does NOT fit Quadrajets with Electronic Mixture Control Solenoid (MCS) Note: "44K" is not stamped into rod, this rod does not have any identification stamped into rod shaft. this did not work. Seized/rusted idle mixture screws. Idle Mixture Screws Not Working? Hi, new to the forum. If your car does not have the system hooked up properly, it could overheat on a hot day when you’re stuck in traffic, which could reduce the life of your engine. 090 and idle restrictions to. Here is an old trick. OEM quality idle mixture screws and springs for automotive and marine Rochester Quadrajet 4 barrel carburetors. this is for you eric wuebker - how to adjust idle mix screws on your carburetor properly (since i have never done this on a running engine on camera) holley. Is the fast idle screw on a quadrajet the 1 near the choke on an angle where you put the phillips head screwdriver onto it, or is the fast idle screw the 1 on the bottom of the carburetor near the front down low. Many times I find the idle mixture screws about to fall out! After four turns out with the idle mixture screws, if you still have a lean fuel condition there is a problem. It can be removed if not needed for a computer or for idle adjustment. Other info about the troubled carb: The choke is opening all the way when warm. One of the two idle mixture screws now shows a measurable difference when screwed in, the other doesn't. At 3 it was almost willing to idle, at 4 it was better. Each has a special marine carburetor fuel-metering system calibrated specifically for the unique engine loads found on watercraft and J-style vent tubes to direct fuel and fumes back into the carburetor for safe operation in rough waters. (If you can get them out!) I used a 10" long 5/16" piece of aluminum rod and cut a notch in the end with a file to use as a mixture adjusting tool. The idle mixture screws are installed next. The air mixture port activates based on the proximity of the throttle plate to the port. Now drive the truck. The idle mixture screws are located in the base plate for superior idle quality. On some float-type carburetors, you can adjust the air-fuel mixture and engine speed at idle. It might not work any better than the Edelbrock but I'd like to give it a try. Honda Motorcycle Carb Adjustment Tips Once the engine begins to misfire, back the idle mixture screw out just until the misfire stops. Many people are confused about how idle air control valves work. The basic idea of adjusting the CVK carb is to set the air/fuel mixture screw to provide the highest idle setting possible. All factory Q-Jet idle mixture screws are steel. I actually ran into a friend at the drags one day many years ago. Idle mixture adjustment: Adjust idle mixture screws to lean best idle. By turning them you allow more or less fuel to flow past the needle. Rebuilding mine PARTIALLY cleared up an issue where the idle mixture screws had no effect. The computer is the brains of a computerized engine control system and sensors are its link to what’s happening under the hood. This chart is intended to be a helpful guide when troubleshooting your carburetor. Repeat the operation on 2 and 4V carburetors. Fuel pressure should not drop below 2. If the idle screw is to high, the mixture screws will appear to not work because fuel is being pulled through the cruise circuit instead of the idle circuit. In the old days it used to go that a rich fuel mixture will make the plug go black and a lean one would make it go a chalky white color, optimum burning will make your plugs go brown. QuadraJet Idle Problem from corvetteforum. The Carburetor Idle Circuit and Adjusting the Idle Mixture. It is sitting on SBC, 9. Some other shop installed it but could not make it run correctly. The idle soured up, and by the time it got warm it idled SUPER high, at around 6,000+ RPM. Check out this Quadrajet article that will help with adjusting, I would start the idle screws out 1. Right out of the box minus setting floats idle and opening the mixture screws 1/4. They simply control the amount of fuel and air mixture that is delivered at idle. I only adjusted the idle mixture and speed, and off to the lake. The Quadrajet is a progressive four-barrel design with an air valve actuated secondary circuit. Most of these steep-taper screws are brass. That includes some 1981 & later GM vehicles with Q-Jet carburetor and some 1981 & later Ford vehicles with automatic overdrive (AOD) transmissions. OK, so here it is. -IF all checks out, set the base idle and then turn the idle mixture screws all the way in and come back out 3 COMPLETE turns on each one (many people confuse a 1/2 turn for a complete turn, if the screw is a flathead and you start straight up and down, the next time you come to straight up and down is only a 1/2 a turn) With the vaccum gauge. Check solenoid operation. 020" (if set correctly) so very little idle fuel can pass thru that square opening. It can be removed if not needed for a computer or for idle adjustment. If not, clean the carburetor and work the butterfly with your hand to loosen it up. Turning the air screw out allows more air through the idle circuit, effectively leaning the idle mixture. Other carburetors may have a 4 corner idle mix adjustment (4 idle mixture screws). The idle mixture screws in the throttle plate receive their fuel through the main metering jets. Do the same to the other side and then repeat the process one more time. Unfortunately there is no data that can match the idle mixture screw to a specific carburetor number, so the idle screws are listed by size. Idle Speed Screw Throttle Linkage Main Valve Choke Plate Idle Mixture Valve The carburetor is the heart of the small engine. I have ran into a problem that i cant seem to track down. The most common cause of rough idle quality in engines equipped with this carburetor is an unevenly adjusted idle mixture circuit caused by incorrectly adjusted mixture screws. Reason, the "boob's" who rebuilt the carb many years back for me, enlarged the primary jets. Adjust throttle screw till it reaches about 6-700 rpms and work the mixture screws till a smooth idle. '89 Olds Custom Cruiser wagon (Caprice) 5. I have been going through it trying to get ready for the strip on Friday. The midrange is checked by speeding the engine up to about 1/2 throttle. download rochester quadrajet carburetor troubleshooting free and unlimited. 1 Tuning Your Carb for Best Performance – Rochester 4GC Rochester 4GC Carburetors – Information and General Operation When designed, the 4CG used as small a venturi as possible to keep air velocity high and as such allow efficient metering of the fuel. US manufactured and ethanol ready. 1 Tuning Your Carb for Best Performance - Rochester 4GC Rochester 4GC Carburetors - Information and General Operation When designed, the 4CG used as small a venturi as possible to keep air velocity high and as such allow efficient metering of the fuel. When trying to adjust the idle screws, The engine did not change until the screws were, almost all the way in, or many turns out. This advances the timing about 20 degrees at idle, allowing the engine to cool down to normal operating temperature. I have a 350 Chevy small block with a Rochester quadrajet 4mc fed by an airtex E8(090)? fuel pump with 38 gph 7-8 psi all infront of a power-glide 2-speed. Hard to see. If not, then the carburetor probably needs to be cleaned. The idle mixture screws cannot meter more fuel than the main jets/rods will. Most of these steep-taper screws are brass. The idle set screw is just barely opening up the throttle valve. Finally set the idle speed with the adjustement screw so it idled around 650 rpm in Park. Just count the turns as you re-seat them so you'll know how far to. My quadrajet #17083244 is extremly erratic every vacumm plugged. MIXTURE ADJUSTMENT ALL ENGINES. Toggle navigation. Repeat the operation on 2 and 4V carburetors. - posted in Engine: Ok Rusty the Torana is up and running but I have a small problem with the quadrajet. com, Cliff? and many other sources. Once the idle speed is up, you readjust your idle mixture screw to lean out the engine for curb idle. if the engine was. The engine is idling to high (1000 RPM or so in drive) when warm with the choke open. The first time I crank it everyday I flip the switch to acc, pump three times, and without touching the gas pedal it cranks right up. getting fuel correct led to a bad engine. The engine will not idle with the mixture screws out 1. #1409 & #1410 ONLY) IDLE MIXTURE SCREWS Left screw for left side of carb Right screw for right side of carb FUEL INLET for 3/8” hose (Except marine models #1409 & #1410 which use a 3/8” inverted flare fitting) CANISTER VAPOR VENT (#1400 Only. Start the car.