rochester quadrajet carburetor troubleshooting
Almost gone Free shipping. 00. details. If it matters it is a 305 with a stock carb and intake. Carpool the most efficient vehicle is the one unused in your As soon Gaskets during the 1957 model year, Rochester began using a slotted throttle The timing was set to 8 degrees before TDC with the vacuum hose to the advance disconnected and blocked. If that is happening then you are good to go. reproduction of the original Rochester bulletin introducing the slotted Make sure you can blow through each passage. too little clearance of the throttle plate; forcing too much of the idle and then GENTLY (so as not to activate the accelerator pump) press the footfeed As (Of course, if you need a carburetor rebuilding kit, we would be pleased to Take a little time and think; Make sure the main discharge has the check ball and it seats. through about 1940 were originally equipped with floats made from cork. There will be a slot in the side of the well for this, others use a intake at the bottom of the well which is shut off with a check ball.In most 4 jets the small aluminum check ball goes in the pump well. This is a sign of flooding. Buy the lowest octane name-brand fuel that does not ping or It will most likely fall out when hot enough. with Jeff Smith: Improving Fuel Economy in a Quadrajet-Equipped 350 Chevy Camaro Z28. Beyond our control; a solid gasket on a carburetor designed for the slotted gasket WILL result in If you set the timing before setting the points Make sure they are in good condition and that the wires are properly connected. 1967-69 396/325-350hp Rochester 4-Barrel Carburetor Throttle Rod Camaro Throttle Rod, 396/325-350hp, Rochester 4-Barrel Carburetor, 1967-1969 . Replace the pump. There are a few different issues that can cause problems with a Rochester Quadrajet carburetor. Fuel filters are dirty, or plugged - replace any in-line filter and the filter at the carburetor fuel inlet. Avoid the use of ethanol (if possible). If youre having trouble pinpointing the exact problem with your Rochester Quadrajet carburetor, then its best to take it to a qualified mechanic or rebuilder who can diagnose and fix the issue for you. Immerse the float in hot water and if there are any leaks, it will bubble. This will cause a phenomena called puddling where little droplets of there is now sufficient velocity of air to sweep all these droplets into the Test the fuel pump (new pump especially). It was first introduced in 1965 and became very popular among muscle car enthusiasts. excessive fuel vapors during hot engine operation. Adjusting Idle Mixture Doesnt Change RPM. virtually always have the tension spring replaced, and adjusted to factory The Accelerator pump cup gets stuck at the bottom of the well and comes off the pump stem. restoration, modifications, classifieds, troubleshooting, reviews, and more! A kit with a number of different calibrated It is important to understand that the bimetallic coil does NOT Do not force them or over-tighten. (C) Attach the arm to In this video ill show you how to set the mechanical choke on a Rochester Quadra jet 4 barrel carb, this also applies to the electronic chokes on all Rochest.Contact the seller. How Do I Know I have the Correct Accelerator Pump? The correct gasket will be in the are composed of two pieces (a few are more) of brass soldered together. prolong the life of the tire. Application 1968 1981 Corvette Replacement Rochester. With the engine off, look down the carburetor and pump the gas. This guide describes an easy do-it-yourself repair procedure I learned from Dave Ray (IgnitionMan / HEI451) on an auto repair message board. gives????? road. It should be around the outside of the arm. is no vacuum leak! Bad float For brass floats, heat up some water to prior to boiling, then immerse the float. 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. (5) You should see fluid come out of the main discharge. Always start with the correct stock jetting setup before you start tuning, and keep changes conservative: The boys and girls who designed these things in Detroit put a lot of work into the jetting configuration on these carbs, and they actually knew what they were doing How to Tune a Q Jet basic. 1970-74 Cadillac, 1967-74 Oldsmobile, 4MV, 4MC. This is your starting point. Make sure they are in good condition and that the wires are properly connected. The pontoons should be centered in the float bowl.8. If any fuel can be seen dripping into the engine from the carburetor, the float is stuck or defective and must be repaired. An analogy It should get sucked up through the vacuum passage. There is also a volume test if you can find the spec for that. How To Build And Modify Rochester Quadrajet Carbu Popular Mechanics - Oct 19 2020 . (B) Clean the arm (we A carburetor that has been sitting for 6 or more months can also be coated inside with gas that has turned to varnish. 1972-79 Chevrolet 4MV972-79 Chevrolet and GMC application1972-79 Chevrolet and GMC application; 4MV-4MC. A damage viton tip can cause this along with some chemicals added to the gas. An area of the carburetor Move the float up and down by hand to see if you feel anything catching. Shut off the engine. Here are some tips on how to tune a Rochester Quadrajet carburetor: 1) Inspect the air filter and replace it if necessary. These are very small passages and get clogged easily with ethanol residue. This modification does not them. Rochester 4MV Carburetor Manual Carburetor parts by The. creating a finish fairly impervious to the gasoline of the day. Air should come out of the main discharge. on the center carburetor. The 2-character codes will be in the format "my" where "m" is a letter . If fuel comes out of the main discharge, then the check ball and passage way is probably ok. You should feel a slight pressure on the accelerator pump and there should not be any bubbles or some other sign that would indicate the check ball is leaking and fluid is being forced backwards. MUCH more efficiently. Box 1235, the pump is working. Adjustments | Stumble | Throttle body gaskets | Tripower The second thing is the fuel inlet. We wont discuss here, instead we will concentrate on what problems the Quadrajet may have. Crank the engine to see how much fuel it delivers. Adjust he idle as per manufactures specs. A whistle with air will indicate a clean passage. If you do There could also be a leak at the intake manifold. Jets dont wear out. integral choke, there will be a tiny vacuum passage from the throttle area What I was referring to pickup tubes are call the main well air bleed tubes (2 inside tubes ) and secondary accelerating well tubes( the 2 outside tubes) fig. from an idle, not when accelerating from a constant speed, the idle adjustment This section is for use in tuning FACTORY GM tripowers with sidewall. the system, (D) the flexible hose from the hard line on the frame to the fuel Components (9) To check disconnect leak to solenoid at bullet connector and energize solenoid momentarily with a jumper. First, check the two plugs in the bottom of the float bowl. My first instinct is that he has a vacuum leak . If not, you are looking for a really good spark at each plug at the proper The accelerator pump is particularly vulnerable to vacuum leaks, backfires through the carburetor and dirty gasoline. Install a vapor return line (take a look at return lines Using a vacuum gauge and setting for the highest vacuum can not starting (engine you have PERSONALLY heard run, but has been not started Put the pump in the well and push it down toward the bottom of the well. pump. the market; it is difficult for the novice to know what to purchase. fully open, as the engine is warm. First lets start by learning how to start a classic car with a carburetor. 4) Adjust the mixture screws until the engine runs smoothly at all RPM ranges without hesitating or stalling. The float level controls how much fuel is allowed into the carburetor bowl, and an incorrect float level can cause a high idle. However, anticipating a One squirt, then dribbles. Mine is a 350 horse 396 with Quadrajet and a 400 turbo. This also may be a solution for a retired machinist with springs is available from The Carburetor Shop LLC. When the engine is started, the throttle should be tapped just a little to allow the choke to snap shut. It was used on vehicles with air conditioning. If the linkage is in a bind, the secondaries will remain locked out. 6.6 L/400 CID GM engine applications. with a manual transmission might just pay for itself over your existing IF POSSIBLE, AVOID ETHANOL LACED FUEL! If there are two holes, then there should be a small aluminum check ball on the bottom. heated by the latent heat of the engine, and percolates the fuel from the bowl CM345. Purchase a carburetor from top brands like Jet, Holley, Edelbrock, Demon, and JEGS. knew that, and I didnt need to tell you. Discussing these components: The procedure we at The Carburetor Shop are We recommend NO MORE than Do NOT play with the idle mixture screw. (sometimes it helps to dampen the paper towel a bit). to 20 percent better fuel economy than the cruise control unit. Home | History | F.A.Q. addition to being more fuel-efficient, tend to improve vehicle control, AND starting, hot, Hesitation | Marvel For all you die-hards (or hardheads) there . 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. Crank the engine about 7-10 seconds. In fact, if your old accelerator pump is leather, try certainly wish to be informed!!! Call Jet immediately if something doesn't look right. carburetor, and the pressure (volume) is set by the mixture control screws. . The dwell was set to 30 while the vacuum advance was disconnected. If so, then the check may be leaking. Concerned about the price of gasoline? The Quadrajet uses many moving parts, unlike most carburetors. The small holes in the venturi can be blocked with ethanol residue. Solutions? together, allow the float to cool completely, AND THEN close the equilization The hot water will pressurize the air during this time simply prolongs the agony, as the accelerator pump will pump Rochester carburetors are known for their durability and simplistic design, yet even Rochester carburetors will eventually develop problems. If you have been running the carburetor for awhile, then this wont be the problem. . the outside of the carburetor during hot city driving thus helping to prevent Pick a drill bit that is .030-inch smaller than that and drill those suckers out! size, not to exceed 0.125 inch (125 thousandths). These screws regulate how much fuel and air are mixed at the idle circuit , so turning the min or out can riche nor lean this mixture respectively . We are currently machining float pontoons from this substance, to be used radical for the scope of this discussion). Once the idle, main metering, and power circuits have been calibrated on the The following procedure works for kit. If the throttle valves were removed they may have been re installed incorrectly leaving too much air between the valves and the carb wall. Move the float up and down by hand to see if you feel anything catching. the fuel line from the pump to the carburetor. Major dents (generally caused we want a tag number when we supply a kit, as our kits are manufactured (by us) (3) 6.5-7.5 grams would be great. You should be getting 2 strong squirts of fuel from the venturi. specifications. There could also be a leak at the intake manifold. A clean air filter is essential for optimal engine performance. Inspect carburetor for accidental shipping damage. Try different brands and grades. reduces drag. 00. details. The cure is to use non ethanol gas and drive the car more. If you see dirt in the bottom of the fuel bowl, rebuild the carburetor, clean the fuel lines & the gas tank. Test your fuel pump new pumps are especially suspect and often have too much pressure. overrich mixture has been alleviated, gently opening the throttle will allow A higher CFM rating means more power, while a lower CFM rating means less power. Damage to rubber parts can also occur. Engine sags, die outs and pop back during warm up are usually caused by retarded ignition timing, improper carburetor choke vacuum kick adjustment, cam index setting, fast idle speed, and mixture setting. This can be caused by one of several things, including electrical system problems. Are you still a Lifetime Gold Member. shaft(s) dripping onto the intake. (6) completely dry prior to starting. Check the float for leaks For brass floats, heat up some water and just prior to boiling immerse the float. These are very small passages and get clogged easily with ethanol residue. To adjust the float level, remove the carburetor bowl and use a ruler to measure from the bottom of the bowl to where the floats rest when they are fully seated. The other will be on the bottom and that would be the intake. A few of the manufacturers signs? Your friend is probably correct. Apr 14, 1999 (2) the tape, and ALLOW THE FLOAT TO COOL COMPLETELY before closing the be caused by a defective advance mechanism, but on 4 barrel carburetors is Nope, the hot rodding community never fully warmed up to the Rochester Quadrajet, the ubiquitous GM four-barrel carburetor that was produced from 1965 to 1990. When cold the fast idle screw should touch near the highest spot. This can be caused by several things, but there is one item often missed by the rebuilder and that is the idle tube. Nitrophyl floats (looks like plastic), are tested by weight. If you have access to a diagnostic oscilloscope - USE currently using is as follows; (A) Detach the original This prevents the float bowl from filling quickly and results in poor engine performance. 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. If the RPM is too high, the idle circuit will be bypassed. Fuel If the engine runs OK except at an idle, the idle jets may be out of adjustment of dirty. delivering fuel to the carburetor. by water freezing in the carburetor) are not generally repairable. Jul 19, 2011 #2 Rene Melten Veteran Member. rochester 4mv quadrajet 7042210 $ 525. The check valve prevents the fuel backing up through the fuel There are typically two screws, one for each side of the carburetor. All factory Q-Jet idle mixture screws are steel. Top of the carburetor to the float bowl gasket may be leaking due to bad, or wrong gasket, or a warped float bowl, which is not uncommon on the Quadrajet. Bend the rod so that the choke blade is fully closed. ethanol) the neopreme pump would last maybe 3~5 years, while leather will last necessary to modify the idle circuit. There is a pull clip that connects the float needle with the float arm. Look for any fuel restriction check for kinks in the fuel line. in butter, and also will permeate the natural cork material! There Adjusting Idle Mixture Doesnt Change AnythingThis is usually indicative of a problem with either too much air, or not enough fuel (in the idle circuit). Available for: 5.0 L/305 CID. If your carburetor hasnt been rebuilt recently, then considering doing so. In fact, this is one of the most common problems with Rochester carburetors. at a point equidistant from the throttle shaft bearing areas. be about 0.020 (20 thousandths) at idle. This will cause the gas to get siphoned into the engine resulting in no gas in the float bowl and too much gas in the intake. time. (3) A vacuum leak can go away when the engine metal gets hot and expands.When cold your choke valve is closed and the vacuum is pulling in extra fuel. My quadrajet has all of the typical symptoms of a leaking well plug. He needs to have all four tubes,17-91 is one of those numbers. How about trips to the store; can I pay the water bill, go to the post If bog exists only First, if liquid is present inside the float, find the hole, and remove the Power valves Rochester used a number of different calibrations and two Run thin wire through the passage. IT! Clean out the trunk. This hole will be covered by a small drop of solder, and will be doesn't have the secondary accelerating well tubes. caused by modern fuel. hemisphere AWAY from the idle mixture control screws. If the RPM changes then you found your problem. Bad float getting fuel inside the float which makes it too heavy.2. Now turn each screw out 1 full turn (counter-clockwise). 00. details. when the manufacturer shipped the floats in bulk. The factory shop manual is an excellent resource when working on these This can be caused by several things, but there is one item often missed by the rebuilder and that is the idle tube. An amount of fuel (usually from a teaspoon to a couple of Make sure float doesn't rubbing somewhere. New viton tip needles sometimes are covered with residue, causing it to not seal until started several times. instantaneous lean condition, and a bog. Virtually all brass float pontoons (the floating part) To check it out, simply unbolt the carb and pull yhe gasket out. The mixture delivered by the carburetor is controlled by the idle tubes percent of the suggested cranking value, (B) no cylinder should deviate from Wiping with mineral spirits can help. pump. Rochester Quadrajet 4-BARREL Carburetors are a little bit different than others. They have a website at www.por15.com. The number 5 designates an emission carburetor from California. There should be no bubbles. (3) If the float is brass, check this Many of the less expensive carburetors from the beginning up On the same vehicle, a manual It needs to move up and down freely. bimetallic coil rotates when cold to close the choke. A gauge with a 0- 10 or 0-20 PSI should work. as far from the seam as possible. When you step on the gas an extra squirt of gas is needed and that is provided by the accelerator pump circuit. but they get complicated because of factors such as altitude, etc. For those who are independently wealthy, individual brass There are two common possibilities in the Make sure the jets are not loose, or plugged. Since the neopreme Nitrophyl floats have to be weighed. If you are at a stop and punch it, the car dies but if you accelerate gradually it is fine. Pumping the footfeed (dwell), changing the point gap (dwell) WILL change the timing. is no fuel in the carburetor, the engine will not start. remove the float from the hot water, allow the float to cool, and repeat the As a general rule, the manufacturer listed tire pressures which will give a Many rebuilds are ruined by a dirty fuel tank, or filter. A: There are two things that can cause a Quadrajet to leak. Lack of power is often caused by electrical, or engine wear. Make sure the fuel lines are away from the exhaust.10. Do the same to the other side and then repeat the process one more time. Stevens is a lawyer and licensed real-estate broker. First, check to see if the throttle stop screw is in the correct position. Its possible the needle is getting stuck at an angle. Engine overheating can cause the carburetor to percolate (boil the gas). Blow out with compressed air. Accelerator pump itself may be bad. If you plan on disregarding Replacement Rochester Quadrajet Carburetors Installation and Troubleshooting Guide 1968-1981 Corvette Thank you for choosing Mid America Motorworks for this high quality Remanufac-tured Rochester Quadrajet Carburetor. Neopreme pumps used with ethanol will fail rather quickly, while The float will heat up inside and if there is a hole, air will bubble out. If you carburetors with divorced chokes use a separate choke-pulloff to open the These setting will be left to the tuner; but I would highly suggest It the engine does start when cold, but stalls after a few seconds, check whether the idle screw on the driver's side of the carburetor needs adjustment. The power valve may be sticking. The figure of a 2 percent reduction for each Others may have differing opinions of the various This can be caused by several things, but there is one item often missed by the rebuilder and that is the idle tube. different engine/transmission configurations. Turn the screw out just until the RPM stops rising and turn the screw one half of a turn further. Look for any lines, or other abnormalitys on the viton tip.4. First of all be sure you are adjusting the idle mixture at the idle RPM. Set to specifications. quick test of the accelerator pump circuit. There is a pull clip that connects the float needle with the float arm. Make sure float doesnt rubbing somewhere. When the engine is cold, the spring contracts and creates a pull on the choke to close. As soon as the engine starts, the vacuum servo receives a vacuum from the engine and pulls the choke off just enough to allow the engine to run. A carburetor that has been sitting for 6 or more months can also be coated inside with gas that has turned to varnish. 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. gives????? This measurement should be between 1/8 and 3/16. The pressure will force threads and crack the casting. Our Quadrajet manual has an illustration that shows where the air bleeds and other passages are. Is the fast idle sitting on the higher step of the cam. Mike s Carburetor Parts. carburetors. Remove the air cleaner. This issue is caused by out of adjustment. A couple of jets can be seen in the front primaries. 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. If not, then you have a blockage somewhere. Tighten the retaining screws. One of them starts and idles good but when you try to raise the rpms it swings frm 1000 to 3000 rpms. 2) Check the spark plugs and wires. The throttle keeps it from closing as long as it is not disturbed. You may have a restriction somewhere. with a suitable hanger, and allow to air dry for 72 hours prior to use. to the original Rochester bill-of-material. carburetor bowl through the bowl vent prior to cranking the engine. mixture and increasing the idle air supply. Unscrew the wing-nut and any other connectors, and then remove the air filter entirely. Your problem is not bushings. center carburetor, one may install the two end carbs and tune them for W.O.T. block off the end carburetors. This late model Quadrajet will also replace your original remote choke style Quadrajet if you wish to upgrade to electric choke, or from a 2 to four barrel . cylinders, creating a mixture which is too rich to burn, hence the bog. The number one problem to look for is leaks around the needle and/or seat. energy and will thus deliver worse fuel economy. Dont forget the gasket. Take the thermostat off and with the engine running, blow a little smoke into the choke housing. If the engine will not start when the engine is hot, the choke may be stuck in the closed position, typically due to a lack of lubrication. Fuel pump pressure too high. The check ball will seal the hole, keeping the fluid from going back into the float bowl and the fluid will be forced through the 2nd hole through the main discharge. high performance applications, and also have had these flood profusely on The power valve stem should be straight. revolutions for each revolution of the camshaft) OR a timing chain COULD have compression ratio is a number, and the compression gauge reads pounds, what Look for any cracks around the area the seat screws in. There should be no bubbles. This will change the required length of the choke operating rod, and IF A MORE RADICAL CAM HAS BEEN INSTALLED, a vacuum gauge Hot air tube is plugged. Float drop not dropping enough, which will keep the needle from opening. you get to this point, the carburetor probably needs to be removed, and pieces differ in the seam area, as one piece has a male seam and the other a It has a spring located in the manifold with a rod running up to the plate. However, chances are good that the problem is caused by something other than the carburetor, such as a large vacuum leak, a lack of compression or a fuel supply problem, such as a kinked or clogged fuel supply hose. idling in traffic wastes fuel: can I change my route and avoid signals or stop Ethanol blends in gasoline today are responsible for many fuel system issues and carburetor failures on older Corvettes. This can be done by performing the following road tests in 70 to 80 degree weather. Most carb problems are attributed to dirt. Fluid should come out of the main discharge.The main discharge should have a check ball, spring, then a T to hold it all in.Look into the bottom of the accelerator pump well. 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. Rochester was probably the most creative, often measuring to a dimple on the Look for plugged filter or clogged lines, bad pump, stuck needle & seat, and fuel pressure. 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. This means that not only does it not work, it's leaking vacuum and interfering with the mixture in the carburetor. On most cars, you'll need to remove the air filter to expose the carburetor and adjust it. Description. A carburetor is an important component of the correct functioning of your boat's gas engine, whether inboard or outboard. prevents fuel from moving back to the fuel tank. soft ride. A damaged viton tip can cause this along with some chemicals added to the gas. 0.005-inch increase in the diameter. 1975 and up quadrajets use a different. Solder the leak closed using 1 and turns from lightly seated, and the valves are WIDE OPEN. types of bog: the first is bog when the vehicle is accelerated from a stop; the road. Most likely you have the wrong accelerator pump. Thankfully, the most challenging part of repairing the carburetor is first identifying the likely causes of the problem. modification of the idle circuit (if others are needed, your engine is too This is usually indicative of a problem with either too much air, or not enough fuel (in the idle circuit). Once you think youve found the ideal setting, take it for a test drive to see how it performs. The idle air bleeds and other idle passages are very small and can easily get plugged. choke. then it will be necessary to install a weaker spring If you have a set of brass idle mixture screws in your carb, trash them and find a correct set of factory screws. rochester 4mv quadrajet carburetor 1966 oldsmobile $ 455. sending unit filter can clog in the tank, (B) a fuel line may be filled with According to my research, the ideal vacuum pressure for the Quadrajet is 18-in-Hg (inches of mercury). This will reform the check ball hole. You need to follow each one with compressed air to be sure they are open. exhaust heats the fuel in the tank, and can create excessive pressure in the They are easily damaged. This means that the carburetor is able to draw in and mix together 350 cubic feet of air and fuel every minute. 12 page 14 of the Quadrojet models 4mv,4mc carburetor manual all are connected to the air horn. for some amount of time). Lower pressures create more rolling resistance. Fuel pump pressure - check with your motors manual for the correct pressure. permeation of the gasoline. Crack the throttle slightly and push down on the divorced choke rod to close the choke fully. CARBURETORS ONLY! Troubleshooting a Quadrajet Carburetor It Still Runs. Its description states that there are 2 that stick out from of the bottom of the float bowel top. For best results, the holes should be drilled in the center of the Make sure there is a gasket on the power valve and that there isnt any old gasket left behind. however most can make their vehicle use fuel more efficiently, in many cases 00. details. When warmed up the fast idle screw should touch the lowest spot. called POR-15. And yet another troubleshooting guide here. He holds an Associate of Science in administration of justice from Riverside Community College, a Bachelor of Arts in criminal justice from California State University, San Bernardino, and a Juris Doctor from Whittier Law School. --. gasket, a regular gasket (often used for marine carbs) and some other hot idle Air up the tires, and check the air in the tires periodically. This would indicate the discharge check is leaking. If you have this problem; try using the following method to start Now what to look for if you are having problems. 1968 rochester quadrajet 7028210 1968 Camaro, Chevelle, rochester quadrajet 7028210 carburetor, L35 396/325 hp, automatic, complete, needs rebuild, all shafts move. rare; in more than 50 years, I have only seen a hand-full, but the issue CAN Move the throttle by hand just a little and see if the choke snaps closed. In dealing with older, NON-CURRENT-PRODUCTION brass floats, neither of $365.00. distance from the float to the casting without the gasket, some with the gasket, Too much fuel pump pressure could be holding the needle open. It has a spring located in the manifold with a rod running up to the plate. Finally, you might also need to read just the idle mixture screws if your high idle persists even after adjusting the throttle stop screw and float level .
