carburetor stumbles off idle

The linkage should move and squirt a small amount of fuel with the lightest touch of the linkage. When I give it throttle, it kinda makes a sucking air noise and stumbles. Be sure your running the proper fuel pressure. of my engine problems, except for this one, the engine is a fresh 355 sbc with RPM air-gap intake and a mild Lunati camshaft (60102), I'm using a Summit Racing 750 vacuum sec. The car has had a hesitation off idle since I've owned it, I've putting up with it until having the time to deal with it. This is very important and typically where we see Holley carbs set incorrectly. Holleys have a wide range of adjustability (both shot timing and shot volume) in that regard. If it does then you probably have something wrong with the diaphragm setup. JavaScript is disabled. Thats what causes the bogging and poor throttle response. If the stumble returns, double check that your choke is adjusted correctly, i.e, the paper clip trick. My question is are you sure your vacuum readings are right? Email any other details needed. Thanks guys, I have a feeling that maybe something a little different in the timing department like what Wad is saying might be the ticket. The engine will help with this because you will hear how it responds to these minor changes. Maybe a bad assumption though. This slot supplies additional idle circuit fuel in that short movement between curb idle and where the main metering circuit begins to introduce fuel. If your car or truck is equipped with a Holley four barrel carburetor and stumbles upon acceleration, more than likely the carburetor needs an adjustment to the accelerator pump assembly. (Jets,Rods,Springs). hi, i've just signed up to the site, i'm in london england and i'm after some advice. Once they get too heavy, they will start to sink and let too much fuel in. Wipe the needle viton tip off with mineral spirits. Idle Doesnt Kick Down When Coming to a Stop. Add and subtract then bench test the pump action. This carb seems to run great in all areas except right off of idle and if you get into the throttle a little bit at low RPM in 4th gear. You Connect a vacuum gauge to a manifold vacuum source . Nov 15, 2019. Your email address will not be published. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. As to drilling, as the hole is very small; best to use a "pin vise" and a drill from a 61~80 numbered drill set. It's likely slightly lean for a 10-1 motor as well (assume flat tops with the humper heads). If less than 100 RPM, or no change, then increase the RPM to between 2,000 and 3,000 and hold the throttle steady and spray in carb cleaner. I have 15 deg of mech advance for a total of 35 deg - all in by 2800 rpm. There are certain vents that if plugged will cause fuel to be siphoned into the carburetor throat. A forum community dedicated to hot rod owners and enthusiasts. Float level set to:10mm. Use the specification from the instruction sheet. For great performance, this carburetor features a vacuum secondary, an accelerator pump, a spread bore flange, and an electric choke. Percolating Engine stops and gas boils over After turning off the hot engine look down the carburetor to see if gas is still flowing into the bore. Now with the linkage eliminated pump the throttle. Hesitation off Idle. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. You must log in or register to reply here. Helps make tuning very easy. The answer is amazingly simple. Black is too rich, white is too lean. A compression test has all 6 cylinders within 10% of each other averaging 115 psi. This can be fixed by doing a rough adjustment. You must check this with the vacuum advance disconnected. The car is a '70 Duster, full weight, 4-speed, and 3.23 gear. We transferred the new Edelbrock intake and carb to the new engine. easy to fix if you know how. Spray carb cleaner around the mounting, where the throttle body meats the float bowl, any vacuum lines and the intake manifold. Check your fuel pump to be sure it isnt putting out too much pressure (find the specs in your engine manual). Next, check the spark plug wires. Engine speed should be 2000 RPM - 2500 RPM after about 10 seconds. One of the air tubes may be plugged causing a rich condition.Move the float up and down to see if you can feel any resistance. Start by increasing the fuel nozzle size up by three sizes. Before moving any further, make sure the cam is set to . The metering rod fits too loose in the main jet. When a vehicle is running rich, the fuel-to-air ratio is off because the carburetor is delivering too much gasoline. She stumbles and hesitates under normal acceleration. If you don't know what an accelerator pump is, it's a squirt gun for fuel. . [ame]http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf[/ame]. JavaScript is disabled. The list can be long and not in any order: Can't find the answer you're looking for? Back it down until it looks like a perfect square. Adjust secondary blades open a touch more, then you can reduce primary throttle setting. Otherwise this will also cause the engine to bog. The consent submitted will only be used for data processing originating from this website. Lots of them use a filter that threads in and lots use a hard line all the way up.What is this hole? Off idle stumble/hesitation 2.) Obviously the carburetor isnt getting gas. Now he serves as a regular contributor to OnAllCylinders. Wipe until you dont get any black.Dirt may have gotten into the needle and seat. Holley recommends the No. Your AED Carburetor is hand built, test run and double checked for performance right out of the box. Light throttle stumble, Holley carb. Learn how your comment data is processed. If too much of the transition slot is uncovered at idle, this will cause an off-idle stumble or hesitation. Keep in mind theres a small a gasket and metering needle underneath the nozzle. -replaced accelerator pump twice. Disconnect the link that connects the throttle shaft to the accelerator diaphragm arm. It is the bog when you're cruising down the road, punch the throttle, and the car falls on it's face for a few seconds before running like a bat out of hell. 5-7 psi rings a bell. Problem now is I can't rev it past 2-3k rpm. This is normal for the Carter YF & YFA. If the RPM smooths out, then you found your leak. The float drop should allow the needle to drop down enough to let fuel in. Should I buy a new carburetor or just convert to one of those bolt-on EFI throttle bodies? Thanks. Do not plug it off. Discussion in 'The Hokey Ass Message Board' started by Mr. Sinister, May 6, 2011. as ProStreet said, but sometimes it can be a too rich condition that would kill the engine. Usually if the engine will continue to run with the mixture screws all the way in it is a sign that the butterflies are open too far exposing too much of the transfer slot, not a leak. Look closely at the float and float pin. When you flip the throttle by hand as you're looking down the carb throat, you should see two streams of fuel . Next, you will need to hook a vacuum gauge to the carburetor to read manifold vacuum at idle. with a 4.5 pv, then built a 700 dp with the stock 6.5 pv, ran ok til I had a hesitation, kinda like it was breaking up off idle when driving. My accelerator pump diaphragm leaks around the housing. There is definitely gas being squirted in from the accelerator pump, but after that the engine will bog down unless more gas is pumped in (by tapping the pedal multiple times to get more from the accelerator pump). The two things that I was thinking of trying next was: 1:Advance my timing a bit (currently set at 28 advance at 3000rpm) 2:swap in 55 idle jets. Also test your vacuum reading. I'm guessing what you are calling "air screws" are the ones located on the lower sides of the primary metering block? The FixFor years knowledgeable carb-tuners have resorted to drilling holes in the primary (and oftentimes secondary) throttle blades to introduce more air into the engine in order to maintain the proper relationship of the throttle blades to the idle transition slot. This allows maximum fuel to flow through the nozzle. Most people experiencing hesitation think, "put in bigger jets" right off the bat. Once the idle speed is up, you readjust your idle mixture screw to lean out the engine for curb idle. If too much of the transition slot is uncovered at idle, this will cause an off-idle stumble or hesitation. Ask me how I know. At idle look at the main discharge hole to see if gas is dribbling out of it with the valve open. Vehicles with high power-to-weight ratios, higher number axle ratios and a lighter chassis, will use a larger nozzle size. If not, then it is keeping the throttle from closing. Work the throttle to see if the throttle plate closes. Does anyone have any hands on with these carburetors. 12. Not sure , but tried several times to set the 4 corner screws with very little positive results. '75 and '77 models use stock Keihin Pilot Air Jets - size #110. After reading, I noticed the OP says he has the XE294HR. Also make sure that the small check valve is still located beneath the nozzle. Rpm's go up and down, car shakes at idle, and it has lack of acceleration/power. Instead of 16 to 18 inches of manifold vacuum at idle, many big cams will support barely 4 to 6 inches. A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. The Fora platform includes forum software by XenForo. The overall objective is to deliver the right amount of fuel. The Fora platform includes forum software by XenForo. Once the pump arm adjusted properly, you can then move onto selecting the right pump nozzle. You've finally installed that lumpy cam in your big-block street-stormer, and you're ready for the testdrive. sec. Robert recommends a replacement jet - size #98. This should not be happening. when riding shifting is smooth. -very slight vacuum leak on driver side of throttle shaft. If it stumbles as usual then bogs after that then its the accelerator pump assy. May 13, 2014 If it has enough overlap for a loping idle, fuel injection wont have enough vacuum to not be a pain in the butt to tune. 1998 Chevy Z71 Full Size Pick-up Vortec 350. no, don't put anything on the threads. PLEASE SEND HELP! Weve seen this work very well. I tried adjusting the accelerator pump to act a bit sooner, which did help, but also appears to have a negative affect at the higher rpm band. Check for vacuum leaks. though which is a much different animal than an Eddy. The metering rod has its own spring and clip witch hold it in its own place, your adjustment is that part only. Make sure the accelerator pump linkage moves the arm to the diaphragm as soon as the throttle is moved. Before you start the engine, examine the fuel bowl side of the throttle body. I have been trying to get it working again for about 2 . The Kibbe and Friends Show: The Price Is Wrong! Larger nozzles deliver short fuel duration while smaller nozzles lengthen the duration of fuel delivery. duration. I would agree that the jets (primary) are off. So now Im thinking to much fuel when the throttle is beyond mid-point. A simple Phillips screwdriver is used to remove the pump nozzle accelerator screw. I may order a pair and try them out this year as well. Make sure your vacuum advance isn't leaking. Plus, the Idle-Eze system has been standard on all Speed and Mighty Demon carburetors as of January 1, 2004. You shouldnt be able to blow through (using about 5 lbs).Run thin wire through all of the small passages. Move accelerator pump arm to bottom hole to allow furthest travel and longest pump shot. Test the fuel pump pressure. air fuel meter will help determine these easily. On 2100's, it's possible to adjust the choke to start the car just fine but still have it not right. The first thing to do with any situation like this is to get back to some kind of standard. This slot is exposed to manifold vacuum as soon as the throttle is opened. New points, coils, plug wires and boots. I am looking to purchase a Carter rebuild kitPK105. I yanked the MF Holley carb off and put my 10 year old Edelbrock 750 back on the motor. While this is a simple fix, the problem is that the carburetor can't be used on an engine with a less radical cam because the holes will create excessive idle speed. Cure The Bog And Sluggish Response On Your Holley Four-Barrel Carburetor, By Properly Adjusting The Accelerator Pump Assembly, How To Tune The Power Valve In A Holley Carburetor, How To Choose A Regulator For Carbureted Vehicles, The Inside Scoop on Deb Halls Detroit Speed Built 1971 Pontiac Firebird. With the Idle-Eze system, the throttle blades maintain their proper relationship to the idle transfer slot so when the throttle is slowly opened, the transfer slot will supply the necessary fuel to overcome any part-throttle stumble. Most noticeable in the street avenger series. They tend to absorb over time (years). Wadd2 those are the bushings I was referring to. If I lift on the pedal or if I go harder on the pedal it will recover. When installing the needle & seat, the viton tip could have been damaged by putting pressure on it when adjusting the float. VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. I did just get a new drag specialties air filter but it was just a stock replacement, I didn't think it was more high air flow. Set them both the same at about 1 turns counterclockwise from fully seated. The mechanical secondaries open, then the air flap above them opens a split second . when riding shifting is smooth. Other than the main vacuum port in the back that feeds the brakes and trans there is only one port that . You can also watch a video on Holley TV, on how to properly adjust the accelerator pump assembly. Mine is the comp. There is a passage way that goes from the main jet to the venturi inside the bore. Make sure that it is clean and clear. By chance if this carburetor was transplanted before this all started then the problem may be the carburetor main jet is too big. Off-Idle surging is a common occurrence after installing a carburetor. Jun 11, 2009. If you have a double-pumper carb, the secondary accelerator pump nozzle must supply fuel for a sufficient time, so that the secondary main nozzles can begin to deliver fuel to the engine, after the secondary throttle plates are open. . . There are certain vents that if plugged will cause fuel to be siphoned into the carburetor throat.Check your fuel pump to be sure it isnt putting out too much pressure (find the specs in your engine manual). An problem here would allow the gas to bypass the needle & seat. If you have the MoCo svc. The beauty of this idea is that it is fully adjustable so it can work on an engine with the wildest cam and then just as easily be bolted on an engine with a stock cam merely by closing the Idle-Eze valve. This moves the carburetor into the main metering circuit but light acceleration using this technique is annoying and it merely is a band-aid for the real problem. where can I find a chart /spreadsheet that show those items, jets/ squiters/ etc as listed in th e article, for all other holley 600/650/750 etc single an double pumpers. My 2100 carb wants to stumble/die just as I leave idle. Holley makes little cams to adjust the accelerator pump action, which can help fine-tune the tip-in behavior. For the YF probably around 4 lbs.The needle in the needle and seat may be damaged. 1986 AMC Eagle Wagon 4.2L/4.0L head, AW4,NP242, Chrysler 8.25" rear. There is like no resistance while turning the air screws. Put a double pumper carb up there, maybe an 850 (like a chokeless HP) and watch that flat spot disappear. Jeff, this is a great write-up. Start with a 0 line and if we multiply 10 X .140-inch this would be 1.40 inches which would equal 20 degrees (10 times 2 degrees). You are using an out of date browser. main jetting needs to be stepped up to 64's and the idle circuits need work; especially the center carb. We often see where the adjustable spring is set incorrectly. later, KrustyTC. You shouldnt be able to blow through (using about 5 lbs). First, locate the idle mixture screw. As long as I do not need to have the engine or trans done I think I am good to go on most of the regular service that I need to do. goldduster318. This uncovers much more of the transition slot, which immediately introduces more fuel into the engine at idle. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. Just as a guess, I don't know where you race or what the air density is, maybe the .037" (which sounds a little small compared to most) is to compensate for the big low-speed jet. Place the housing between 2 flat metal stocks. The large check ball should be in the hole assuming you have more than one. You can try wiping off the viton tip with mineral spirits. Manage Settings I originally thought the problem was insufficient fuel which is why I did the the rebuild. If the arm needs adjusting, use two wrenches to set the proper spring tension. Thats what causes the bogging and poor throttle response. you might have a hole in the accelerator pump diaphram. The most I can get out of mine for vacuum is 7 or 8 in park! This will be trial and error by adding and removing washers. The float pin could be worn causing the float to hang up.Check the main discharge. Typically the idle speed is the only adjustment needed however this short reference guide is intended to explain the correct method to set-up your new AED carburetor. Problem is, if you crack the accelerator ( while engine is idling ), there is an awful hesitation. Gas could be coming in the bowl around the seat. Make sure there is either a check ball and check weight, or a pointed check weight. 2023 HOLLEY PERFORMANCE PRODUCTS, INC. ALL RIGHTS RESERVED. Bike stumbles at idle to 1/4 throttle. Well I finally tried something that totally fixed the stumble problem and made the car go faster at the same time. The idle screws turned full in is usually a sign of an internal leak. http://www.stevesnovasite.com/forums/showthread.php?t=201545, http://4secondsflat.com/Carburetor Sizing and Series Charts.htm, http://www.demoncarbs.com/Tech/DemonSelectionGuide.asp. Lightly seat the mixture screw, then 2 turns out. The carburetor is a Holley 750 with vacuum secondary. So what's the fix? SOLD. I had to do four things to correct the off idle hesitation: 1.) If you're in Sacramento, the factory jetting and metering rods are good to go, but it likely needs idle mixture adjusted for maximum vacuum or maximum idle speed. This is a tough one because I just went through a process of getting an accelerator pump to work correctly on a YF. In addition to this circuit, there is a tiny slot cut into the throttle opening on the primary side (and on all four barrels if the carburetor is equipped with four-corner idle mixture adjustment).

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