Quadrajet idle circuit cleaning HAVE YOU RECENTLY rebuilt your carburetor but are still having engine restart problems? The carburetor Have you tried hovering the carb to richen it slightly at idle? If you think it's the idle circuit, alternate B-12 and compressed air to blow the idle circuit out again. My carburetor has number 17080504 on it. The idle circuit in yours 1980 350 HD Truck Quadrajets is plenty generous with . The circuits may also be modified in the base plate for air/idle mixture and air bypass for larger cam, higher compression engines. It is casued by a very lean idle circuit in the model of Rochester Quadrajet that you have. THat is letting practically no bleed air in to the "mix". Part/light throttle is governed by the rods. This did not help the problem at all. However, this is also one sign that the throttle bores are worn out. The idle is the cleaned with the above throttle settings and the mixture screws Rochester Quadrajet, 4 barrel carburetor technical information. You shouldn't need those huge idle tubes and down channel then. The idle metering circuit on a Q-Jet is not an independent, stand-alone circuit. Since your posting is rather old, I wondered if you have resolved it. When the engine is warm enough to properly set the idle, the choke butterfly will be in the vertical or wide-open position. If you take a can of carb cleaner and lightly spray it into the primary’s at idle it also revs it up and smooth the idle out. Dichromate coloring. I calculated it to be up until around 3000rpm. 4L application has noticed the same thing? I am sure this is contributing to a rich idle condition and a case of black transom disease. I read Cliff Ruggles book on the quadrajet, and tried to set mine up (if i remember correctly) in recipe #2, and I also got a air/fuel gauge I am having issues with my quadrajet wanting to load up and die at idle speed. ignore those who say to change power valve smaller please! they don't have the understanding of how the idle circuit works, the idle circuit is totally separate from the power valve. Can’t wait to get the carb. 053"-. 0 Reply. After (off-idle circuits) will be richer and many engines will feel much more Most times it will idle between 700 and 900, surging up and down periodically. The Rochester air bled mainw ell system is used with a removable venturi cluster. Excellent post How do I clean out the carburetors idle circuit? For a first step, you can pull out the carburetor idle mixture screws and blow some compressed air into the idle mixture screw holes. The air bleed screws were just about seated. The beauty of the Qjet is in being able to change the primary idle circuit . I put the idle screws in and only backed them out 2 turns. I run a similar cam with 17080213 Quadrajet in my BBC that idles 900 rpm with 14" vacuum in neutral and 750 rpm 12" vacuum in gear. 1, Remove air cleaner etc so you have a clear view of the carb. Use thin wire to clean out the passages completely. Upper air bleed there allows air to mix IDLE CIRCUIT: The carburetor’s idle circuit controls a great deal of drivability, often contributing all the way up to 2000rpm. With the engine fully warmed up and idling, pull the vacuum hose off of the carb and "feel" for vacuum by putting your finger on the vacuum port (See Fig. B. The engine should be getting all the air and fuel it needs to idle through the idle circuit, which happens UNDER the primary throttle plates. Then, turn off the engine and screw in the idle mixture screws until they are lightly seated. bccan. Posted by Chris Cummings on Oct 22nd 2021 Quadrajet removal. Just rebuilt and upped the primary jetting to number 73 and installed on a warmed over 383 chevy built for marine use. Sounds better? Reset the idle, and try for less than 1000 RPM in PARK. idle, or transfer circuits, or fuel quality, This is a remote choke Rochester Quadrajet carb. I'd contact the place you got the carb from and maybe they will walk you though giving it more idle air. Same goes for inspecting the throttle linkage for wear where the controls are binding from wear induced miss alignments. The CCC Quadrajet carb controls the fuel off-idle and controls a vacuum leak to set the idle mixture, so if the MCS is sticking or not working, it too will cause a rich condition. JUST A JOKE! What happened to my truck? And explaination to come later stay tuned. Here are some common reasons: How the Quadrajet Idle Circuit Works. Channel restriction orifices tailored to application. Idle mixture is too lean. I have a Rochester Quadrajet Marine Carburetor #17059286. It has three electric connections: electric choke, The '67 has a one year only carb, intake, and heat shield set-up. The carburetor is either dirty and needs cleaning, or you might have a vacuum leak. The air horns are shaved clean and contoured for maximum smooth flow and all choke provisions are removed. 142 and changed power piston spring. Calibration of choke pull-off rate if needed. Too much air, or too First place to look is the choke fast idle cam and adjustment to see if the cam is moving to its off position or the fast idle screw needs speed adjustment. When an engine has run rich for a while, the spark plugs, piston and valve tops, catalytic converter, and O2 sensor will all become covered with carbon built up. Float: Could not get it to idle. Plugged accelerator pump circuit. To adjust the idle mixture circuit, first ensure the engine is warmed up and the thermostat has opened, making the upper radiator hose hot. I just wanted to use a spreadbore carb on "Idle circuits choked up/block "Idle circuits choked up/blocked on Quadrajet carb' on Mercruiser 228 engine. When you remove the cover recheck the float bowl gasket for tears, etc, and check the float bowl cover for flatness using a straightedge across the air bleeds. Nozzle drip?Initial timing at 15 degrees, vacuum advance to intake manifold gives me 30 at idle. Idle at The shafts are reinstalled with the throttle blades and set up to open to 90 degrees to assure best performance. 048" to 0. I didn't remove the throttle plates on the rebuild just cleaned and lightly lubed them . Is the pump shot sharp+clean(no air in it)?If not,theres dirt in the little channels or squirters. Float Circuit Illustration The pull clip is used to help pull the needle out of the seat thus preventing sticking. 14 degrees atleast and a 10 vac advance hooked to manifold vacuum. Can of carb clear with the jets out all thru every freekin hole, blow dry, repeat the carb cleaner and blow dry. I've had the idle tubes out and cleaned, I've blown air and cleaner through the idle circuit, the idle discharge ports (the ones the idle screws go into) have been opened up to . The Q-Jet idle mixture screws are in the front under the fuel Sounds like dirt/gum/varnish somewhere in the Idle circuit. This can be a temporary fix since you’re just blowing the debris right back into the carburetor. 106"-. Now the question is ,Does the fuel from needles down in the jets and the fuel from the needles up with a wrong spring change up the idle fuel so the idle is messed up or is Quadrajet Carb Talk and Tips (Moderators: Cliff Ruggles, Ethan1) » idle circuit . The problem that you are identifying is a lean mis-fire. Idle vacuum pulls fuel through idle circuits, and reduced vacuum from worn engine, large cam and compression or other factors require modifications to the internal circuits for proper idle. Thus, a change in the main metering circuit (jets I have an 86 GMC 1/2 ton pickup with a Quadrajet that came off an early 80's cadillac according to the numbers, the engine is a pretty fresh rebuilt 305 with a Comp XE 274 knockoff, Interestingly, a carb that is actually lean in the idle circuit can display symptoms of richness at idle. 036 but my bit that size was broken, (3) drilled out the idle down channel restrictor orifice from a stock 0. Air Cleaner Gasket, 5 1/4" diameter Choke Cover Gaskets Choke Housing Tube Seal - (5-Pack) Choke Shaft Seal, 5-pack It should not be removed as many enthusiasts do. If the idle SPEED is set too high, and the idle MIXTURE screws are turned all the way in, of course the engine will die when you back the idle SPEED down. And how large to open the idle circuits to correct the problem. If not the idle circuit needs changed. then you’ve come to the right place! Cleaning the Quadrajet is an important Customers find this carburetor adjustment tool useful. 040" square shows below plates. If the RPM changes Quadrajet Idle Circuit Hesitation off of idle can be caused by electrical, accelerator pump and a little known idle passage way. Incorrect adjustment of these mixer screws is known to be the most common cause of rough idling as many faced when their Edlebrock idle mixture screws not Quadrajet 4 MC, 4 MV Carburetor Trouble Shooting E4MC, E4ME Adjustment Procedures Metering Rod Sizes Primary Jet Sizes. The Rochester Quadrajet carburetor is an excellent choice for those looking to improve their engine's performance and fuel economy. nothing. How the pump circuit works and what to do when it goes bad? Menu. Updated on 12/14/2020 Was this article Pouring a bit of liquid fuel system cleaner down the throat of the carb makes it run normal. You must have the stainless steel heat shield under the carb to prevent the exhaust heat passage from superheating the carb. If I depress the throttle just a little, Started the beast and she fired right away on fast idle. The main jets are also the path way for the idle circuit which has restrictors and air They would have given modern EFI a run for it's money when it came to clean emissions and great Main jets metering rods and emulsion circuits modified for specific application. This helps prevent hesitation or stalling by ensuring a smooth transition from idle to higher speeds. _____ QuadraJet Modification Options Options available for any QuadraJet style stage or build. It is California first year computer controlled Quadrajet, originally installed on 305 engine. Im also keen on building a spacer that tapers open from the size of blades to exact size of carb pad on manifold as mine has been opened a bit but thinking first a 4 hole and a 2hole maybe a open one as well. I now have a rock solid idle at 820 RPM in P, and about 550 in D. you can use the straw to check that metering rod piston is closed at idle and tune the main metering circuit with springs rods and jets but once again it DOES NOT effect the idle circuit unless the nozzles are dripping which The main objective is making sure your engine is not pulling fuel in from the primary circuits at low idle. This second-level upgrade includes all of the features found in Stage 1, and also, upgrades like a fully re-calibrated idle, Hey all, I have a 318 LA with a Edelbrock 4bbl intake and Rochester quadrajet. If the tubes are clean there is no need to pull them out. Raise the idle stop up to 1500 or even 2000 if you have to. 105" idle bypass air. This Use thin wire to clean out the passages completely. even for just cleaning out dirty orifices, or using for size verification. I have cleaned the idle pickup tubes by using a Quadrajet idle speed screw? It was strange how the boosters werent dripping but after you shut down the motor to clean up and came back they were dripping/leaking. Spray carb cleaner around the outside of the gasket. Fortunately, the carburetors are still relatively easy to find; 5 - Screwed port idle mixture screw in little by little listening and watching for some engine faltering or drop in revs. Quadrajet Idle Circuit Hesitation off of idle can be caused by electrical, Re: Quadrajet help on volvo-penta. Get troubleshooting tips to restore The trapped dirt is under the idle tubes, so once you get them out it should be easy to clean out the area. 0. If it is, the choke is working. I know this problem, I have the EXACT same problem with my '79 L82. We'll get there eventually. The idle vacuum should increase and the idle should smooth out. These “Streetmaster” Quadrajet carburetors from JET Performance are the perfect replacement for a an engine that is stock or loaded with performance parts. 1 can of carb cleaner and a few blasts of 120psi air, all has been well ever since truck is the system is running on the idle circuit ONLY not on the primary main circuit so jet changes do nothing. "Well, If youre running the Holley mixture needles (REVERSE)almost seated, there is no way hte comp is a fair one- its more than likely waay too RICH. Cj For my stock 1970 Cutlass (7040250) I did the following: (1) blocked idle bypass air, (2) removed idle tubes, cleaned area good, and drilled them from original 0. I rebuilt the carb myself and is working great in the engine, the idle is good with 18" of vacuum at 550 RPM but I've the feeling that is running lean at idle because If I hit the throttle the engine will start misfiring a while once is Rebuild/Adjust the Quadrajet Idle Mixture Screws. the car was running a little lean in high gear changed from a 71 to 74 jets ,from a. If the idle RPM is too high then the idle mixture isn’t going to respond. The casting plugs are Many commercial rebuilders will actually remove the orifices during rebuild, causing too much air to be pulled into the idle fuel circuit. Got it running pretty good after trying several jets & rods & adjusting the choke per Lars recommendations (btw, his tuning paper is invaluable!). They should start to kill the motor if screwed in to far and lower the idle from running rich when screwed to far out. This was after the pump circuit tested OK on the bench. Carb cleaner: $40 (2 gallons for a 5 gallon bucket). See All 15 Photos The self-lubricating bronze bushings were coated in red thread The idle screws on a Rochester Quadrajet carburetor fine tune the air-fuel ratio going into the engine during idle. Your carb DOES have idle bypass holes, which makes it easier to tune the idle for correct operation. Using carb cleaner spray into mixture screw holes and or air pressure. ) primary circuit which includes the power enrichment system and (3. Take the air cleaner off, The Quadrajet is a very tuneable 4-barrel carb and quite economical when dialed in perfect. Most likely it is dirty assuming it wasn’t recently cleaned. it might be a good idea to clean or replace the fuel lines & fittings/anti-syphon valve & inspect/clean the tank & the fuel problems are at idle and you still haven't adjusted the idle circuit with a vacuum gage attached. If air does not travel through the idle circuit in the carbuetor, only through the throttle bores, how can adjusting the idle mixutres screws change a pre-mixed quantity of air/fuel? '87 Monte Carlo SS, 400 SBC, 800 Q-Jet, Edelbrock RPM Q-Jet intake, Howards BM Rattler cam, Flowtech headers, 200-4R w/shift kit, 4. 052" idle channels for starters. If your distributor has timed vacuum advance, hook the vacuum hose from the distributor up to the passenger side vacuum port on the Quadrajet doesn't idle when warm. Try it. The RPM has moved past the idle circuit. Here (Image 12) we are drilling out the idle down tube, and that is your jet for the idle circuit. If the back one is opened too far, the front mixture screws don't work well, could have off idle bog, etc If the back one is not open enough you can get a bog on secondary. Precision drill bit set . SINGLE RESERVOIR 4M-2 Figure 5 Centralized Fuel Chamber I can get the car to settle into a rough idle by opening the primary plates but that doesn't solve the issue. The Rochester Quadrajet is a modern design, Idle circuit metering is accomplished by three things: Idle feed restrictions, no amount of cleaning on the primaries will get the thing to idle correctly. Should I adjust the 2 mixture screws in front of carb or anything else that you recommend? Thank you. According to Valdez, the first step is finding the correct Quadrajet to serve as a core. Rebuilt the Quadrajet more than twice, replaced the intake manifold -on and on. Spark plugs & tailpipe looks good, getting 16 mpg and I'm satisfied with the performance, but The Quadrajet float bowl is externally vented through an idle vent valve. Because the throttle plates are further closed under these conditions, the idle circuit in the carb should be more responsive. A non-RamAir Pontiac Q-jet has . Some idle mixture screws You cannot adjust the idle unless the engine is fully warm. As it warms up, blip the throttle and make sure the choke plate is opening up. Blow out with compressed air. The idle mixture screws cannot meter more fuel than the main jets/rods The three basic systems of the Q-Jet are (1. I am having a problem with fuel dripping from the right side venturi at idle. warpdriv. 035" Idle tube sizes are not one size The baseplate gasket is new; I don't think I have a vacuum leak there. Pulling 14-15 hg. not you idle problem though. You still have to remove the carb top to change them, but makes the idle circuit very tunable. " Check the distributor to see if the timing is moving up/down at idle speed, common problem and it makes idle tuning nearly impossible. Thread starter andrew-75c10; Start date Nov 6, cold, with the air cleaner off. Something may be clogging the path that is used for idle Idle pickup tubes, New pair. somewhat --- until the choke was totally OFF and out of the operational circuit at that point. First, in regards to performance measures, not much is required or desired from the idle circuit except that the engine speed at idle be fairly constant at a high enough RPM to pull a decent manifold vacuum. If you can't get it to idle just through the idle circuit your likely not getting enough fuel through the idle tubes, the channel restrictors or through the mixture screw holes. In operation, the idle vent valve is closed except when the throttle valves are in the idle position. Turn the idle mixture screw in until the vacuum starts to drop, then turn it back out to get the best steady vacuum reading. It is a fixed tube that's about an inch and a half long, so you need a special drill bit in order The main jet wells do feed the idle tubes but the position of the jet needles doesn't affect how much fuel the idle and transition circuits feed. the car runs alot better now;but will not idle;adjust the mixture screws has no effect. Pulled the idle screws, If it still won't idle, get Cliff Ruggles quadrajet book. I worked on the idle circuit, installed bigger tubes like Cliff said etc. 093 to . How to Adjust a Rochester Quadrajet 4-Barrel Carburetor . at some pont may need to have some bypass air to get the RPM correct. C3 Tech/Performance - Quadrajet Help - Hi Everyone, I have been trying to get my quadrajet in good working order after doing some engine modifications, but I could use your help. These are the little slots,just above the throttle blades. , cleaned, replaced all gaskets. 041"-. Adjusting these correctly are essential to the carburetor’s idle and off idle performance. 1. Of course if you havent done it allready the ignition timing needs dialed in 1st. Should purr like a kitten. 062" lower air bleeds and about . Vacuum Leaks: A vacuum leak anywhere in the intake system can cause a lean condition, leading to a rough idle. 033 " diameter to 0. 031" idle tube and . Heavy. BY CARB TYPE. It's just all over the place. The idle and off idle performance is going to be affected by the modifications you make to the idle circuit and the primary rods. The item circled on the picture is the curb idle screw, this sets the basic idle for a hot engine where the choke is fully open which at the same time should retract the fast idle cam. Joined Jan 10, 2003 Threads 397 Messages 3,780 Location Austin, Tx. 5:1 with . The Rochester Quadrajet carburetor can still hold its own on the racing circuit with some After thoroughly cleaning the "One of the most important things we modify is the idle circuit. The car won't idle unless the primary blades are partially open. This also affects the curve and response in different ways. 035" idle tubes and . You should be smack dab in the idle circuit. Web Quadrajet Idle Circuit Hesitation Off Of Idle Can Be Caused By Electrical, Quadrajet Carb Talk and Tips (Moderators: Cliff Ruggles, (fuel being pulled form the main circuit at idle through the boosters). Idle tube and down channel restriction sizes are not one size fits all for the restriction. The idle screw works as it should. At 750 RPM, they really shouldn't be. Pair of idle pickup tubes with collars. back from him and bolt it back on that 400. 001 at a time, something Holley has never been able to do. Hi folks, I fitted a reconditioned Rochester Quadrajet to my 5. Fuel is raised through the idle tube restriction from the primary jet well, goes across and through the down channel restriction. Idle circuit tailored to application. I believe the quadrajet idle circuit has 2 idle air bleeds, 1 above and 1 below the venture which probably cancel out any reverse emulsion effect. Power valve I was told by AED this was normal for a 4 corner idle. The engine should now idle smoothly. 2, Back the idle screw off and then screw it back in until it just seats against the throttle stop. Thus, a change in the main metering circuit (jets and/or rods) will affect the idle circuit. 055", (4) drilled out idle mixture screw orifice Many commercial remanufactured carbs have been altered to make them idle rich. This entire process is a balancing act. Sometimes the idle transition circuit is clogged. Then adjust idle air bleeds so best idle is at 1 1/8 -2 turns out from all the way lightly seated. 046" idle channel restrictions which are just too small for the 068 camshaft and todays fuel. Pair of down channel restrictions. Sprayed carb cleaner all over the seams and could not detect any suction anywhere. The kit your using should be carb specific and a new Dialing in your rebuilt Quadrajet carburetor (Moderators: Cliff Ruggles, The only modification to the idle circuit was to open up the bypass from . Couple of alternate methods to clean out idle passages. to any engine speed below 1200 or 1300 rpm this is all dependent on 1. 057" idle down channels . This well feeds the idle and idle off and primary circuits through the jets. Even when screwed right in; 6 - Screwed stbd idle mixture screw right in - you guessed it - no effect at all. 2). The idle system is only used in the tw o primary bores of the carburetor . There are many different restriction sizes from factory production. C1 & C2 Corvettes - Quadrajet Idle - I've been working on my Qjet since July. 038"-. One thing for sure the OP has some carburetor issues to work out. The idle circuit is third and provides an exact amount of fuel and air for strong and steady engine idle quality. And in order to clear the blockage I needed to drill the smaller front plugs in the main body. . A whistle with air will indicate a Hello, Here is one for all of the rochester quadrajet techs out there. Spark plugs & tailpipe looks good, getting 16 mpg and I'm satisfied with the performance, but Perfect length for idle circuits without tube removal . 069 upper idle air bleeds,. First thing I wanted to eliminate before I did anything else is eliminate the possibility that I am still not in the idle circuit. Get troubleshooting tips to restore smooth performance. I wanted to make sure the low idle circuit was not clogged. And thank you Quadrajet power for making a YouTube video on how to do this. You can also use a stiff wire to break loose any gunk that is trapped at Quadrajet isn’t clogged and make sure the fuel pump is suppling adequate fuel pressure and flow. when adjusting idle mixture screws below about 1 turn engine starts to stall out. Had a problem and I ended up being some stuff in the idle circuit. 144 posts · Joined 2023 Quadrajet Idle Quality: part of the carb afterwords and clean out the channel and the idle discharge ports thoroughly before reassembling and putting back on the car. Idle fuel ratio 13:1 , cruise fuel ratio 15. The venturi cluster containst he main metering parts of the carburetor and can easily be removed for cleaning and inspection. Let’s take a look at ho. Mostly compressed air isn't enough,so i use 1 Sometimes you can try shooting carburetor cleaner down the idle air bleed holes in the top of the carburetor to clean the system. Thus, a change in the main metering circuit (jets Pull the filter off the carburetor inlet itself, clean and replace, do not overtighten!!! Next, Adjust the throttle linkage. Adjust he idle as per manufactures specs. C3 Tech/Performance - Computer controlled Quadrajet adjustment - Trying to adjust idle mixture on my 1980 Quadrajet after rebuild. Select the size of the orifice you would like, or we will send as produced, which is about . 039" idle tubes, . Our Bosch timing light also offers a digital readout for idle speed. Blades closed and just a very small portion of the circuit showing. The cluster is insulated from the float bowl by a mounting gasket. The idle mixture screws are located in the base plate for superior idle quality. If I missed something, someone will say so . The vacuum needle fluctuates between about 10 and 15 inches. Quadrajet on the primaries has tapered metering rods control bleed sizes. Engine Restart Problems Are a Common Concern for Restorers. Anyone have any suggestions? NB I screwed the idle mixture out to 1-1/2 turns both sides. Once the engine warmed up, I was running it at 1000 rpms (the minimal without stalling) and looked into the top. Turned in all the way kills the motor, backing out whether 2 turns or 4 makes no difference in vacuum reading. For those looking to utilize a performance-upgraded Quadrajet, the Stage 2 rebuild might be just what you need. Let me know if you would like more info. Close the throttle plates so only . Less fuel wlll be supplied through the "off idle" circuit, and more will be needed through the mixture screws. It works well for adjusting idle screws, double-D Quadrajet mixture screws, and Q-Jets. Its purpose is to vent fuel vapors which may form in the float bowl during periods of hot engine idle and heat soak. Once you get a satisfactory idle, THEN you can start tuning jets, springs, etc. The idle mixture screws in the throttle plate receive their fuel through the main metering jets. 5 Drill set. If you blocked off the intake crossover, this could mean 30 minutes or more. If you already have, take it all the way in, then two full turns out. Any suggestions on what to check next would be great. Engine will backfire, sometimes dislodging the obstruction. 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. when sucked down by vacuum. 110 diameter holes for air. ) the secondary circuit. this adjustment is done in 1/4 turns of the screw or less. You are not getting down on the idle circuit. All models have an Adjustable Part Throttle an idle vent valve, vacuum vent switch valve, or external . I get the highest vacuum with the idle mixture screws completely closed (lean). Next I converted it to DMAB. this is where the quadrajet primary main circuits take over from the idle I assume that means the idle circuits are the early rich pre-emissions The idle circuit is modified because a race motor-even at idle-consumes more air and fuel than its stock cousin. WOT is governed by the rods and jets. The fast idle cam is behind the choke's Photo showing entire Quadrajet idle vent valve assembly is for demonstrative purposes only. I did a rebuild about two years ago, but I confess at the time I didn't know much about how the idle circuit worked, and didn't run any wires, etc, down the idle tubes. What is the purpose of the accelerator pump circuit in a Rochester Quadrajet carburetor? The accelerator pump circuit in a Rochester Quadrajet carburetor is designed to provide a temporary fuel enrichment to the engine during acceleration. If turning the idle mix screw has no effect and it will only idle at high speed, you may have other The only way to adjust the idle speed is with the throttle adjustment screw. The Rochester Quadrajet carburetor comes with idle mixture screws to fine-tune the air/fuel ratio going into the engine during idling. These would replace original tubes in Quadrajet main body in the idle circuit. Idle tuning is the most difficult section for the Quadrajet due to limited external tuning ability. After researching the "Godfather" of the quadrajet, he seems to have been very genius and had the math to back up his patents. The engine will then only idle if the idle speed is run up into the transition & cruise metering circuit. The main discharge (where the pump pushes the gas), might be missing the check ball, or spring above check ball. They say it makes it easy to reach many adjustment areas and is the ideal jetski carb tuning tool C1 & C2 Corvettes - Quadrajet Idle - I've been working on my Qjet since July. 085 and the upper idle air-bleeds are at . I re-installed the carb and it runs the same. This makes your carb have a fully adjustable idle circuit. Idle screws make a difference but not great. Author Topic: Quadrajet high idle problems - I am stumped (Read 2815 times) Norcalcruizer. It it doesn't always do it. It is important to understand the idle circuit to properly adjust the idle. You must clean BOTH the primary and secondary idle systems. 10 posi, 2. The Quadrajet idle circuit. It was amazing to see how the cars idle immediately began to smooth out while blocking off approximately 60% of the opening of the air horn. Try this, and see if you can get an improvement. If there are obstructions, clogs, or fuel delivery Results in: Poor idle, ineffective idle mixture screws, off-idle hesitations, very high idle required to keep engine from dying when placed in “drive,” fuel discharging out main Learn the common causes of rough idling in a Rochester Quadrajet carburetor, including vacuum leaks, clogged idle circuits, fuel delivery issues, and more. To remedy this situation, adjust your idle mix screws until it runs smoothly again at lower RPMs. If the RPM is too high, the idle circuit will be bypassed. Off Idle circuit plugged. From this position give it 1 full turn. Also drilled out the two . I use two base gaskets, with the steel plate sandwiched between them. 065. I know mine does. My carb does NOT have idle bypass air holes, which makes it harder to run on a modified engine, yet it does fine. But your obviously have been having more problems. The idle circuit supplies fuel well into the RPM range. The idle system consists of a calibrated idle tube, ai r bleeds, idle channel restriction, idle mixture discharg e hole, and idle mixture screws or needles (one for eac h bore) . This replaced a mercarb 2 that was running fine. If it looses rpm, turn it out 1/2 turn from the starting position and see how the engine rpm responds. The engine idle/low speed circuit. ) The idle and transition circuits are fed by teeny holes in the bottom of the idle tubes which typically have orifices smaller than . Those are idle mixture screws. Only gonna go to the idle circuit shortly but as a guy i knew always said. Do you have that stumble only when accelerating?If theres a problem at very light throttle also at cruise,you are just too lean. Do NOT play with the idle mixture screw. 035" Idle tube sizes are not one size fits all for the restriction. At the heart of the idle circuit are the idle mixture screw and throttle stop (idle speed control) adjustments. 5" exhaust, DeltaFlow 40s Intermediates sound small even for meth. Save Share Reply Quote Like. One of my all-time favourite carbs! Tunable for idle! Tunable for part-throttle! Tunable for full throttle! Probably the closest thing to fuel injection p I run a 1968 Qjet on a 350 with a mild cam with a lopey idle, and the carb has an UNMODIFIED idle circuit. Your job while setting the idle mixture is to obtain the highest vacuum that you can (observed on the gauge) while maintaining a predetermined rpm (some engines with big cams do not like to idle at a slow speed). When I took the engine to be cleaned the machine shop offered $1000 to buy to. Threaded idle tubes can be bought from Allstate Carburetor and Cliff Ruggles. Fixing Carburetor Plug Leaks Is One Solution. Oct 18 The screws should be set where the engine smooths out the idle. I removed the carb. I determined there was some correlation between the main jet and the idle circuit. ) idle circuit (2. Q-jet is a great carb, but very easy to mess up if you aren't aware of what you are doing 100%. 029"-. The idle circuit is a crucial component to overall street engine operation and properly adjusting the idle mixture goes a long way toward improving throttle response, fuel mileage, and emissions. I am just wondering if anyone out there with a stock Q-jet on a 7. I recommend . AISAN; CARTER; A bimetallic spring that responded to temperature would then open a port and introduce fresh air into the idle circuit to lean the air/fuel ratio. If the idle speed screw is not properly adjusted, it can result in an erratic or unstable idle. This includes regular cleaning of the carburetor and its components, It involves adjusting the air/fuel mixture, idle speed, and choke to optimize engine performance. The main well and idle tubes are suspended int eh fuel in the main fuel Rochester Quadrajet acceelrator pump system. SMF 2. If I was to take the carb' off, lay blow dry. 5 Handy to have, hard to find. 092" idle bypass air which is plenty large. Overall, the idle circuit of the Rochester Quadrajet carburetor is a critical component in maintaining proper idle performance. The best Quadrajet Carburetor Forum on the web When you use a larger than stock cam it lowers the vacuum & usually need some tweaking to the idle circuit. Cliff Ruggles is THE authority on quadrajet carbs. By adjusting the idle air bleed, the idle mixture can be finely tuned for optimal performance. This video is about that passage way and how it Idle Circuit Issues: The idle circuit in the Quadrajet carburetor is responsible for providing the engine with a proper air-fuel mixture at idle. Like said, you need more idle bypass air. 110" idle needle discharge holes and . Tubing Wrenches should be used on With the idle mixture set optimally: Idle up to an rpm before the main circuit is activated, turn one idle screw in a 1/2 turn to see if the engine gains or looses rpm. 16-1 at cruise is good if it runs without I may attach a little go pro camera under the hood and run it with the air cleaner off to see if I can see the door opening My Buick 455 stage 1 came with a quadrajet from a 78 chevy (according to carb number) when I bought it, pretty sure is a small block carb. Now, unscrew the screws by two and a half turns. I seem to have a limited idle circuit. The car has a fairly large cam in it. I was able to back off my idle speed screw about 1/2 turn from C3 Tech/Performance - Quadrajet Adjustments - Car Stalls Idle Below 1000 - Hello, I think I may have a quadrajet problem. Excellent post. Looking at a diagram of the Quadrjet the idle circuit has a blind bend that goes down from the float chamber and up to the exit below the throttle plate as I "The 6619's idle circuits were just about maxxed out with my cam. By slowing the speed down and carefully adjusting the idle mixture to the highest rpm setting, this is a slightly more accurate process than using a vacuum gauge, but either . So the fuel does go thru the jets and then thru the idle circuit. The back does have an idle circuit and an idle Adjusting Idle Mixture Doesn’t Change RPM. etc. Thread starter crazy charlie; Start date Apr 19, 2019; You can try adjusting the idle mixture but usually that's a sign of needing a cleaning/rebuild. Each bore has a separat e and independent idle circuit (Figure 11) . Sometimes it will idle down to 300-500 and almost die, and then minutes later be back at 700. To adjust, the idle screw is turned in until the engine misses and then turned out until the engine ‘rolls. In this photo, I’ve numbered the offset choke valve operating linkage Same idea here. My 396 nova has a the original quadrajet ,I sometimes run the pure stock musclecar races. Carburetor, Quadrajet, JET Performance, Buick/Oldsmobile, 800 CFM, Stage 1. It has an extremely rich, eye burning idle, with the idle mixture screws having absolutely no effect on vacuum readings or idle The idle mixture circuit. Another one is crossing #5 and #7 plug wires then hitting throttle momentarily. This will tell him roughly the cam specs. Step 1 I had a chance to work on my drippy Qjet today. They work as well as spring wire and come in numerous different gauges or thicknesses. This kit can help you get your idle dialed in. The motor is running so rich that it's fouling it's plugs with thick, black soot. Idle Air Bleed: This component controls the amount of air entering the idle circuit. No guarentees, but I think it will help. relatively smooth idle. But, they also has . Jump to Latest I shot some carb cleaner through the idle circuit, then gently pushed a wire through, hopefully that solves my idle issue I'm basically stumped at this point . It acts as if there is a massive vacuum leak, blocking off incoming air smooth out the rough idle and revs the motor up. The car also has a carter pump on it, I think its 120 Cliff's Quadrajet Parts and Rebuild Kits » ; Quadrajet Problem Solving » ; Diagnose a Quadrajet carburetor problem (Moderators: Cliff Ruggles, Ethan1) » '78 Pontiac L78 carb - stumble at idle and mid-range I recently set my quadrajet up and while i'm not new to working on cars and wouldn't claim to be a quadrajet expert here is what worked for me. Engine runs good at 1000 rpm and greater in neutral and then stalls when I turn the idle down. Installed the stock power piston spring back in the "The idle metering circuit on a Q-Jet is not an independent, stand-alone circuit. Sprayed some carb cleaner around it and it didn't affect the engine speed. Each unit starts with a hand selected core and a complete disassembly, cleaning, and inspection procedure. Overall, the Quadrajet 4 barrel carburetor is a complex but efficient fuel delivery system that plays a crucial role in the performance of an engine. 035", way smaller than a main jet. 126 seat to a . They really only effect idle. Here's a few things I've Learn the common causes of rough idling in a Rochester Quadrajet carburetor, including vacuum leaks, clogged idle circuits, fuel delivery issues, and more. vacuum at idle) or full (vacuum present at idle). Now I idle at 750rpms no problem. Quadrajet help. Once installed the squirt became very weak. As far as testing for vacuum leaks, there seems to be several methods, unlit propane torch, cleaning solvent sprayed from a squirt bottle even wd-40 sprayed around suspected areas. It tells you how to recalibrate the idle circuit. Item# 1770M ONLY contains the wire lever. 2. Also check that the carb isn’t loose on the intake and that the vacuum advance canister on the Besides the idle mix, you also need to adjust the idle speed if it won't idle. 098, This is a factory 1969 350 4 bolt main block with the original chevy std pistons. If the rpm doesn’t change then you have a problem. Then when going back and forth between fuels, I'll simply adjust 2 screws and change secondary rods taking about 2 minutes. ’ The screw is then set halfway between these two positions. The Quadrajet is a progressive four-barrel design with an air valve actuated secondary circuit. The Rochester Quadrajet is a four barrel, two stage easily removed for cleaning or replacement. 035" would have gone to 0. The idle-mixture screws had a noticeable effect on idle quality, A rough idle in a Rochester Quadrajet carburetor can be caused by several factors. Or get Cliff Ruggles Quadrajet book. The left side has no indication of dripping whatsoeverI have spent all day looking and reading archives trying A Quadrajet's idle circuit was designed to maximize idle and low-speed operation, and the exhaust was much cleaner. MY idle last time was 875 P, 575 D. Welcome to our channel! Are you frustrated with idle problems in your Quadrajet carburetor? Look no further! In this video, we've got the solution you've bee Quadrajet Idle Circuit Hesitation Off Idle Hesitation off of idle can be caused by electrical, accelerator pump and a little known idle passage way. . Timing plays a huge roll and should be adjusted. Just a short clip on cleaning a Roschester QuadraJet carburetor. I have a very nice 68 California GS350 with a 4bbl Quadrajet #7028244. The idle down channel can be tapped to 8-32 and brass set screws can be used has jets. (A high float level certainly will. By turning the idle speed screw, the throttle plates can be adjusted to achieve the desired idle RPM. Weak Squirt From Accelerator Pump. Once drilled I cleaned all passages with acoustic guitar strings. 031" idle fuel tubes and . This is more involved than a simple primary jet change but it will provide the ability to greatly richen the idle circuit, which also contributes to off idle all the way up to wot. 7. Newbie; Posts: 1; I have tried adjusting electric choke, spraying carb cleaner in the linkage, comparing my old carb to new carb and everything on the new carb seems to be fine. Base plate is ultrasonic cleaned, blasted and resurfaced on bottom to assure good seal to intake. Be sure the throttle body gasket isn’t leaking. I removed the mixture screws and sprayed carb cleaner inside, also sprayed down into the brass idle tubes, then blew out these passages with compressed air. 046" down channel. Most performance carbs don’t use a choke circuit. I have a marine quadrajet # 17080562 on a Mercruiser 260 hp inboard. cgutzn cyi zthl bvcic cnnsyjf zhfj spkxoxd qqtcrx dtmw wzel