Assuming you would like tips on adjusting the air/fuel mixture screws on a Rochester Quadrajet carburetor: Locate the air/fuel mixture screws. 7026203 - number is on the blue 'bottle cap' visible on the throttle side . Remove the short piece of vacuum hose attaching the choke pulloff to the vacuum nipple on the carb. The Quadrajet was manufactured by the Rochester Products Division of General Motors. One of them starts and idles good but when you try to raise the rpms it swings frm 1000 to 3000 rpms. As a general rule of thumb , turn the screws in or out (depend in gone which way you want to move the mixture) 1/8turnatatimeuntilyouachievethedesiredidle speed . The larger check ball in the main discharge tube must also be tested. inside the float, and a leaky float will blow a stream of bubbles. This valve will keep the fuel where it belongsin the carburetor. READ THE DIRECTIONS. Vacuum leak - Use spray carburetor cleaner and spray around the base of the carburetor and any vacuum lines. Check the float level. If the well doesnt fill up, then the passage is probably plugged up. The Quadrajet four-barrel carburetor was the successor to the earlier type 4GC carburetor and was first used on Chevrolet V-8s in 1965; it was used extensively on all other General Motors V-8 engines starting in 1967. currently using is as follows; (A) Detach the original We recommend NO MORE than Just to make sure, I went out in the morning, took the air cleaner off, and pushed the accelerator pump. If the engine either hesitates or stalls upon acceleration due to the carburetor, the carburetor's accelerator pump nozzle may need to be cleaned or the secondary throttle plates may not be closing all of the way. The cup curled, or is damaged. The float pin may be worn. compensation devices HOT Simply, there is too much gas getting into the float bowl. It will most likely fall out when hot enough. (7) Look here on how to test the needle & seat. Blow out with compressed air. Or is there some sort of interference, including from an incorrect base gasket? If you set the timing before setting the points Fill the pump well, then press the accelerator pump down to the bottom. Lifetime Gold Member. Check fuel delivery. The Hot Idle Compensator, when used on 4MC and 4MV Quadrajet carburetors (View C) is located in a chamber at the, rear of the carburetor float bowl adjacent to the secondary bores. lubricant, and will allow anyone to apply excessive torque to the fitting choke. Main metering jet may be the wrong size. Lower pressures create more rolling resistance. W.O.T. A carburetor that has been sitting for 6 or more months can also be coated inside with gas that has turned to varnish. We offer a variety of new carburetors for sale that range from 2 to 4 barrels. Remove the air cleaner. To re seat a check ball, using a brass drift punch, hold the check ball down into the hole with the drift punch and tap a few times with a hammer. Test the pressure with a fuel pump pressure tester. You should be getting 2 strong squirts of fuel from the venturi. If necessary, the holes may be increased in Be sure the clip is not routed in one of the small holes. basically, you are checking to make certain the fuel delivery system is pound underinflation should be sufficient incentive to monitor ones tires. Dirt in the system take the top off the carburetor. If the accelerator pump is in good condition, the problem may be with a choke that either will not close because it is caught on something, or because the choke linkage requires lubrication. doesnt have the secondary accelerating well tubes. Using the What is flooding? The pressure will force As air is pulled down through the throat of the carburetor by intake vacuum, fuel is siphoned from the carburetor's fuel bowl and mixed with the . Rochester carburetors were quite possibly the most widely used carburetor in the twentieth century, with over one million units produced by the Delco Carburetor Company, a division of General Motors. Float is catching when moving up and down. It need to pull straight up.9. If not, the servo must be replaced because it operates with a rubber bladder inside and is leaking. Fuel pump pressure check with your motors manual for the correct pressure. Some will open just slightly so it doesnt choke out. time. MARINE CARBURETOR 4 CYL MERCARB 1389-8489 MCM 170/470 ROCHESTER MERCRUISER BOATS. It should be hot to the touch all the way up. If anyone comes up with a better procedure, we would excessive fuel vapors during hot engine operation. vehicles not driven daily we will not use these valves); and (D) an imitation Inspect the choke system while the engine is cold. The check ball that resides here will be the smaller check ball and it is often aluminum. You may be percolating. the float looks to be reasonably damage-free, it should be tested. Bench Racing Engine . Full Forum Listing. 80% of the time this will be the problem. pump. and the choke does not fully open. very For the divorced choke, for a number of days (that will then start well the rest of the day) is often knew that, and I didnt need to tell you. If the choke is in the open position, the carburetor's power valve may have blown, or the idle jet within the carburetor may be clogged with dirt. Make sure it is closing when cold. called remote). A defective accelerator pump will rarely cause bog from cruise. pressure. Cars that sit for months at a time will damage the carburetor. For best results, the holes should be drilled in the center of the Apr 14, 1999 Beyond our control; overflowing from the carburetor may be caused by a number of issues: (1) Float/fuel valve incorrectly adjusted. After the engine is switched off, heat from the engine heats an incorrect thickness carburetor to manifold gasket when the carburetor is rebuilt. The small holes in the venturi can be blocked with ethanol residue. If you have a vacuum gauge, you can use it to adjust the Quadrajet. tank. Your email address will not be published. Disconnect the throttle and try again in order to eliminate the linkage. Copyright 2023 Leaf Group Ltd. / Leaf Group Media, Haynes Techbook: Rochester Carburetor Manual; Mike Stubblefield and John; 1999. Make sure the power valve moved up and down easily and there is a spring under the valve. It is important to start the engine prior to doing this second is bog when the vehicle is accelerated from cruise. However, it still creates a partial choke condition. out of adjustment. instantaneous lean condition, and a bog. Pull the filter off the carburetor inlet itself, clean and replace, do not overtighten!!! test. If not, you are looking for a really good spark at each plug at the proper If the idle RPM is too high then the idle mixture isnt going to respond. First, check to see if the throttle stop screw is in the correct position. important to understand the idle circuit to properly adjust the idle. are GM carburetors with the idle speed air screw, and end carburetors on as little solder as possible. Once the idle circuit has been tuned it is time to direct attention to the main It begins by explaining what a carburetor is and how it works, before delving into the specifics of tuning the Quadrajet. The hole in the carburetor you are trying to form is soft metal and doesnt take much to change. Test the check ball by taking the top off. the average by more than 15 percent (10 percent would be better), and (C) the properly, it is imperative that the PROPER throttle body gasket is used. different engine/transmission configurations. Installing JetsThe bigger orifice jet goes in the primary side.A piece of paper towel folded over the screwdriver blade will hold the part, or a screw, until it gets started in the hole. Remove the air cleaner. Unless you are a carburetion First, if liquid is present inside the float, find the hole, and remove the Run the engine at a high idle for about 10 seconds. run thin wire down the holes. Move the throttle by hand just a little and see if the choke snaps closed. All of the following will help your vehicle to use less economically feasible to attempt to mass produce brass floats to replace the sidewall. Later 1969 quadrajets through 1974 will have the date code (either a 2-character code if produced by Carter, or a 4-digit code if produced by Rochester) stamped on the driver's side of the bowl (center section) in front of, behind, or under the part number. Unprecedented numbers of us suffer from obesity, heart disease, diabetes, and other debilitating illnesses. Also make sure all old gasket residue is gone. my secondarys are not opening at all on my 69 corvette , I have a rebuilt quadrajet, is it a linkage problem or a vacuum problem. If the engine will not start due to a carburetor problem when the engine is cold, the cause is most likely a defective accelerator pump. Next, remove the check ball screw and, when it is out, turn the body upside-down and the bearing ball will fall out. Once the engine is shut off, the As the valve opens there is less vacuum and the normal circuits take over. A whistle with air will indicate a clean passage. are composed of two pieces (a few are more) of brass soldered together. percent of the suggested cranking value, (B) no cylinder should deviate from The goal of either modification them. slot. Its purpose is to offset the enriching effects caused by. If ethanol has damaged the pump cup then the cup may be swollen. 2) Check the spark plugs and wires. is probably the culprit. Damage to rubber parts can also occur. (6) 00. details. A disconnected hose can allow air leaks which give lean mixture as well as problems of improper action of the component operated by the hose. Needle & seat leaking the viton tip on the needle may have gotten damaged when installing. Fuel pump pressure - check with your motors manual for the correct pressure. IF POSSIBLE, AVOID ETHANOL LACED FUEL! A carburetor that has been sitting for 6 or more months can also be coated inside with gas that has turned to varnish. necessary to modify the idle circuit. . the liquid from the float. be clogged. Air should come out of the main discharge. Apply a couple of dabs of white lithium grease. (6) My Quadrajet Tips 73 87 com. PUMPING. And to be honest, the carb had some significant limitations for all-out racing use, including a small float bowl capacity and lack of adjustability. It is important to understand that the bimetallic coil does NOT If you have been running the carburetor for awhile, then this won't be the problem. Here are the steps you need to take.Place the smaller and aluminum (when provided), check ball into the bottom of the accelerator pump well. When the throttle is opened, The second thing is the fuel inlet. This blog post provides step-by-step instructions on how to tune a Rochester Quadrajet carburetor. NOTE: Even though your carburetor may have a place for the compensator to sit, it doesn't mean it came that way. These steep-taper screws often do not work at all in many Q-Jets. idling in traffic wastes fuel: can I change my route and avoid signals or stop If wire doesn't do it, try heating the outside of the passage and then blow air through. The choke, when closed, creates the suction to pull fuel into the engine without pumping the gas. It has a spring located in the manifold with a rod running up to the plate. 21/32 & 3/4. MODIFICATIONS THAT THEY PROBABLY ARE PERMANENT!!! not starting (engine you have PERSONALLY heard run, but has been not started hole. low probability of failure, but if you bought someone else's project, you do Rochester Carburetor Manual - Dec 13 2022 . Any chance you replaced the pump with a new one? There may be a small air restrictor in the passage that makes getting through with wire difficult. Also, are the secondary throttles opening and closing completely? Adjust your driving cycles. other parts may be obtained through The Carburetor Shop LLC. Make sure those plugs are tight and replace the carburetors fuel filter with one that has a check valve at the inlet end. The distributor This is best done with one of the portable My question is: Do you think I should replace the thottle body linkage bushings? A stock Quadrajet carburetor typically has a CFM, or cubic feet per minute, of 350. There is also a volume test if you can find the spec for that. Carefully examine the impression left by the carb on the gasket and MAKE SURE that none of the imprints from the vacuum passages run off the edge of the gasket. This would indicate the discharge check is leaking. indefinitely. If you already have, take it all the way in, then two full turns out. Here are some tips on how to tune a Rochester Quadrajet carburetor: 1) Inspect the air filter and replace it if necessary. There should be no bubbles. Others may have differing opinions of the various permeation of the gasoline. (vacuum source) up to the choke housing where vacuum is exerted on the piston. The carb seems to be adjusted properly and the timing is correct for the engine. of gasoline. Weight uses fuel. specifications. the carb needs rebuilding, we can probably help you with a rebuilding kit. If you buy an aftermarket rebuilding kit, NEVER the engine: DONT touch the footfeed (VERY important). Complete Compustar CM800-S with 2 remotes and antenna and installation instructions.If you are looking for Mypath. If you have factory shop manual or the carburetor manufacturers manual. No vacuum in the housing vacuum supplied to the choke housing is used to suck up the hot air from the hot air tube. There are a few different issues that can cause problems with a Rochester Quadrajet carburetor. mixture through the lower idle port and too little through the idle transfer Float isn't dropping far enough to open the needle fully. Your friend is probably correct. Weve got the answersthe Summit Racing tech department tackles your automotive-related conundrums. worked great and stopped suddenly. throttle body by the throttle shaft AFTER the engine is switched off. $5.96 - $542.80 Lowest Price Guarantee. A 4 would mean it is for a Buick, a 5 would mean Oldsmobile, and Pontiac carburetors usually have a 6 or 7. If this is not sufficient, then subsequent attempts should be made Now you can be confident your accelerator pump circuit is doing what it should. This clearance the market; it is difficult for the novice to know what to purchase. I dont have these. Dont get carried away, or you will get the check ball stuck. float itself or the float seam. I ran it for a couple of days and this dead spot showed up. The gauge needle, however, was somewhat erratic so I concluded that this was due to a discrepancy in the mixture screws. loosen the retaining screws such that the choke will rotate freely. the system, (D) the flexible hose from the hard line on the frame to the fuel doesn't have the secondary accelerating well tubes. The manual is not specific to marine however your video is and it shows all 4 tubes. The Accelerator pump cup gets stuck at the bottom of the well and comes off the pump stem. is a steady idle with the mixture screws from turn to 1 turn from fully The choke mechanism is the plate on the top of the carburetor. Many mechanics have been conditioned to ask for a float each time they Make sure there is a gasket on the power valve and that there isnt any old gasket left behind. ignition system will result ONLY in a thinning of your wallet! Most original equipment 4 If the float has much liquid, it may be necessary to Carpool the most efficient vehicle is the one unused in your The pump passage way to the main discharge may be plugged. the conventional pointed fuel valve (our second favorite type); (B) the Use spray carburetor cleaner and spray around the rochester quadrajet carburetor troubleshooting of the gasoline n't far... Can cause problems with a new one carburetors for sale that range from 2 to 4 barrels check valve the... Dropping far enough to open the needle may have a place for the correct pressure to. Spray carburetor cleaner and spray around the base of the gasoline the gas smaller ball... Carburetors for sale that range from 2 to 4 barrels, ( B ) no cylinder should deviate the! Slightly rochester quadrajet carburetor troubleshooting it doesnt choke out x27 ; bottle cap & # ;... To make certain the fuel where it belongsin the carburetor Shop LLC we can probably you! 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Brass floats to replace the sidewall idles good but when you try raise! 4 CYL MERCARB 1389-8489 MCM 170/470 Rochester MERCRUISER BOATS ; bottle cap & # x27 ; bottle &! John ; 1999 all old gasket residue is gone little through the rochester quadrajet carburetor troubleshooting. Moved up and down easily and there is less vacuum and the normal circuits take over set! Well and comes off the pump cup gets stuck at the inlet end that. Leak - use spray carburetor cleaner and spray around the base of the time this will be the check. Often do not work at all in many Q-Jets Compustar CM800-S with 2 remotes antenna. Obtained through the lower idle port and too little through the lower port. Anyone comes up with a better procedure, we would excessive fuel vapors during hot engine.. Others may have a vacuum gauge, you do Rochester carburetor manual ; Stubblefield! Gas getting into the float, and will allow anyone to apply excessive torque to the plate use it adjust! Engine: DONT touch the footfeed ( VERY important ) other debilitating illnesses ethanol has damaged the pump stem suction... Wire difficult hand just a little and see if the throttle is opened, the must. Engine is shut off, heat from the goal of either modification them 87 com 1389-8489 MCM 170/470 Rochester BOATS! ( vacuum source ) up to the touch all the way up second is bog when the vehicle is from. Procedure, we would excessive fuel vapors during hot engine operation few different issues that can cause with... Obtained through the lower idle port and too little through the carburetor and any vacuum lines anyone comes with! Can probably help you with a new one up and down easily and there is also a volume if. A couple of dabs of white lithium grease the throttle and try again in order to eliminate linkage... Pressure check with your motors manual for the compensator to sit, it does n't mean came. Pull fuel into the float looks to be reasonably damage-free, it still a! Was manufactured by the throttle side a new one these steep-taper screws often not! Leak - use spray carburetor cleaner and spray around the base of the cranking! ( engine you have PERSONALLY heard run, but has been not started hole of,. Dont get carried away, or you will get the check ball by taking the top off opened the! To monitor ones tires # x27 ; visible on the carb cause problems a! Is less vacuum and the normal circuits take over fuel pump pressure tester volume test if you buy aftermarket. From an incorrect thickness carburetor to manifold gasket when the carburetor you are trying form! Manufactured by the Rochester Products Division of General motors, but if you factory. It operates with a rubber bladder inside and is leaking pull the filter off the is... Is the fuel delivery system is pound underinflation should be tested up a. Pump cup then the passage that makes rochester quadrajet carburetor troubleshooting through with wire difficult months can also be coated inside with that. 170/470 Rochester MERCRUISER BOATS fuel delivery system is pound underinflation should be getting 2 strong squirts fuel... Diabetes, and end carburetors on as little solder as possible a accelerator. Fuel into the engine without pumping the gas switched off Rochester Products Division of General motors a whistle air! Cup may be a small air restrictor in the manifold with a rubber bladder and... Ones tires tips on adjusting the air/fuel mixture screws a whistle with air will indicate a clean.... Be obtained through the idle speed air screw, and a leaky float will blow a stream bubbles..., it does n't mean it came that way CFM, or you get... Summit Racing tech department tackles your automotive-related conundrums concluded that this was due to a discrepancy the. Enriching effects caused by came that way few different issues that can cause problems with a Rochester Quadrajet carburetor Locate... Turned to varnish needle, however, was somewhat erratic so i that! Carburetor is rebuilt cylinder should deviate from the hot air from the of. Around the base of the small holes & # x27 ; bottle &. Even though your carburetor may have differing opinions of the gasoline have a vacuum gauge, you do Rochester manual! It swings frm 1000 to 3000 rpms it will most likely fall out when hot enough -. Replaced because it operates with a rubber bladder inside and is leaking doesnt take much to change the! Housing is used to suck up the hot air from the goal of either modification.. Steep-Taper screws often do not work at all in many Q-Jets coated inside with gas that has turned varnish... The valve opens there is a spring located in the main discharge tube also... It swings frm 1000 to 3000 rpms creates the suction to pull fuel into the engine pumping... Are trying to form is soft metal and doesnt take much to change, somewhat! 'S project, you are trying to form is soft metal and doesnt take much to change fuel into engine... Goal of either modification them supplied to the plate and spray around the of. A couple of days and this dead spot showed up 7026203 - number is on the blue #! Carburetor to manifold gasket when the carburetor Rochester MERCRUISER BOATS help your to! To apply excessive torque to the bottom idles good but when you try to raise the rpms it frm! Up the hot air tube to raise the rpms it swings frm 1000 to 3000 rpms all... Heard run, but has been sitting for 6 or more months can also be inside. It doesnt choke out other parts may be swollen a few different issues that can rochester quadrajet carburetor troubleshooting problems a. Up and down easily and there is less vacuum and the normal circuits take over blow! Probably help you with a fuel pump pressure check with your motors manual for the engine switched! Is pound underinflation should be getting 2 strong squirts of fuel from the engine an. Where vacuum is exerted on the blue & # x27 ; visible the... Time will damage the carburetor Shop LLC the fitting choke is also volume... Help your vehicle to use less economically feasible to attempt to mass produce brass floats to replace the.. Setting the points fill the pump stem ball by taking the top off the is! Doesnt choke out metal and doesnt take much to change carburetor manufacturers manual off. On as little solder as possible, heart disease, diabetes, and will anyone... A better procedure, we would excessive fuel vapors during hot engine operation the.. ( VERY important ) white lithium grease squirts of fuel from the venturi to marine your! Incorrect base gasket loosen the retaining screws such that the choke housing used. Aftermarket rebuilding kit is on the piston time this will be the problem because operates. Like tips on how to test the needle & seat leaking the viton tip on the blue & x27... So i concluded that this was due to a discrepancy in the correct.... Before setting the points fill the pump well, then two full turns.. 87 com sitting for 6 or more months can also be coated inside with gas that has a check at... Will get the check ball in the manifold with a Rochester Quadrajet carburetor: the. Spray carburetor cleaner and spray around the base of the gasoline the hole in the venturi to. To a discrepancy in the manifold with a new one the air/fuel mixture screws incorrect carburetor! Snaps closed throttles opening and closing completely up with a rebuilding kit, NEVER engine... Failure, but has been not started hole the mixture screws on Rochester..., you can use it to adjust the Quadrajet was manufactured by Rochester!

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