Dirt may have entered the carburetor after it was rebuilt. Next, with the engine off, you need to check to make sure the two idle mixture screws are both adjusted the same. VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. 1986 AMC Eagle Wagon 4.2L/4.0L head, AW4,NP242, Chrysler 8.25" rear. Spray carburetor cleaner around the mounting gasket and the gasket that connects the throttle body to the main body. A non vented cap will cause a suction. Jets are probably not the problem unless they are a lot oversized. Heat up some water just prior to boiling, immerse the float, any bubble indicates a leak. How old is the edelbrock carburetor? Bad plugs can cause high end loss of power for sure. Adding gas to the bore will get the engine running, but dies. Check for any cracks in the bowl top.Check the floats for leaks. To find out if this is your issue just remove the idle jets and see if the off idle stumble becomes a flat out bog down. 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). though which is a much different animal than an Eddy. Spray carburetor cleaner into the throat of the carburetor. Adjust secondary blades open a touch more, then you can reduce primary throttle setting. Back it down until it looks like a perfect square. Jun 11, 2009. Check the fast idle. You shouldnt be able to blow through (using about 5 lbs).Run thin wire through all of the small passages. Once they get too heavy, they will start to sink and let too much fuel in. This time it would idle nicely at about 900 rpm. Keep in mind I'm using a Holley style carb. As before the rebuild, it idles great and runs fine until about mid rpm range in every gear. A light stumble only when accelerating from idle could possibly be caused by the idle adjusting screw, #56, being turned in too far. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. The Honda part number for this replacement jet is 99164-601-0980. The passage is small and can plug easily. Assuming the vacuum is OK, you need to determine if you are getting too much gas, or not enough. Most modern carburetors are designed to function with roughly 0.020 (20 thousanths) clearance between the center of the throttle plate edge, and the throttle body at a point equidistant from the throttle shaft bearing areas. . 3.) Sometimes we spend so much time getting the float level correct, we forget about the drop. If you crack the accelerator from about 1200 rpm, there is no hesitation. The consent submitted will only be used for data processing originating from this website. Most people experiencing hesitation think, "put in bigger jets" right off the bat. Place the housing between 2 flat metal stocks. 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. It could be siphoning gas here if it isnt sealing.Jets are probably not the problem unless they are a lot oversized.If you have the black Nitrophyl type of float, then be sure to replace it. If you are installing a #40 or larger pump nozzle you will need to replace the screw with Holleys hollow pump nozzle accelerator screw. Problem is, if you crack the accelerator ( while engine is idling ), there is an awful hesitation. Your needle could be sticking not allowing enough fuel in. Hope this makes sense. The off idle is not even close to the Holley. They have a pretty cool website with a lot of neat info on there. Stumble off-idle tip in 13.0:1 at 100 km/hr (2500 rpm) cruise Good power, but doesn't pull strongly above 3000 rpm Intermittent 15.0:1 lean when accelerating All without the frustration of emptying your wallet. Instead of 16 to 18 inches of manifold vacuum at idle, many big cams will support barely 4 to 6 inches. I have been trying to get it working again for about 2 . 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. This article leaves out a bunch of detail. This is normal for the Carter YF & YFA. This will let you inspect the spark plugs and also will help to make sure there isnt a bad cylinder. Now it has this problem, may have been there all along and is worse now for some reason. I understand that I can unsubscribe at any time. I had the same problem recently with my 2100 after moving from 5600 ft to 700 ft and rejetted it with larger jets and it runs like a dream. When the engine got hot parts would expand and seize. This is usually caused by the idle screw being turned too high on the carburetor. Start by increasing the fuel nozzle size up by three sizes. 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. Check for any cracks, or perhaps the old gasket is still underneath. When you flip the throttle by hand as you're looking down the carb throat, you should see two streams of fuel . Does the throttle valve close completely? Turn the idle screw out until it isnt touching the fast idle cam. reinstall the carburetor and setup your idle system. It made such a difference I was able to go one size smaller on squirters, all though they were still bigger than stock. I actually use a small, broken drill. Idle-Eze throttle plate assm., 650/750-cfm, mech. This will be our starting point. Warning new fuel pumps often have too much pressure. When a vehicle is running rich, the fuel-to-air ratio is off because the carburetor is delivering too much gasoline. Do you have the check ball and check weight installed, or the check weight with the pointed end?Dirt may have entered the carburetor after it was rebuilt. Of course, you could epoxy the holes closed-though that's even more work-but now there's a better way. You dont want to deliver too much fuel too soon, or to little fuel too late. Black is too rich, white is too lean. If, after adjusting the linkage, the engine still sags on light acceleration, the engine is telling you it either needs moreor sometimes lessfuel on light acceleration. I just bought a nice 69 Dodge Charger with a 440 that I got on a really good deal because the previous owner had given up trying to make the engine run correctly. 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. To balance the idle mixture. You back the screws out until it stops raising idle, then go back in about 1/8-1/4 turn. It idles with a heavy lope like it has a big cam in it and it will burn my eyes if you let the engine idle inside the garage. An increase of more than 100 RPM and the . sec. cams XR294HR and it has .242/.248 at .050 duration. The engine will help with this because you will hear how it responds to these minor changes. The late production image is for engines that do not use a vacuum advance. This is very important and typically where we see Holley carbs set incorrectly. Apr 28, 2011. Lots of them use a filter that threads in and lots use a hard line all the way up.What is this hole? This will keep the carburetor from getting to slow idle. VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. How to fix Holley accelerator pump stumble caused by a sudden lack of fuel (or too much fuel) when aggressively opening your throttle. If too much of the transition slot is uncovered at idle, this will cause an off-idle stumble or hesitation. Thanks for the link and the charts! 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. Make sure the choke valve is wide open when the engine is warmed up. Put a double pumper carb up there, maybe an 850 (like a chokeless HP) and watch that flat spot disappear. (Jets,Rods,Springs). Set them both the same at about 1 turns counterclockwise from fully seated. Strong smell of gasoline when the machine is at idle. Now, if the engine still hesitates on mild acceleration, look at the accelerator pump linkage next. You dont need to drill throttle plates. Carburetor Runs Rich at IdleAmong other things check the idle tube to make sure it is clear. One of the defining features of the AVS2, is the annular b oosters in the primary venturi.With a specific calibration for improved off-idle and cruising performance, this carburetor eliminates the hesitation - and subsequent frustration - associated with a mismatched or poorly tuned carburetor. It doesnt matter as long as youve assembled the pump correctly, the pump has its own spring and retainer clip witch hold the pump in place. This is the accelerator pump diaphragm drain. Just wipe until you dont get any black on the towel.Test the main discharge to make sure it is sealing when not in use. Gently move the float up and down to see if you can feel any catching. Well, forget that silly notion, the jets have nothing to do with it. Manually raise the float to see if you feel any catching. Failure to check that or setting that clearance any smaller will result in rupturing the pump diaphragm. We and our partners use data for Personalised ads and content, ad and content measurement, audience insights and product development. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); The Easy Mechanical Valve Lash Procedure Part 2, The Easy Mechanical Valve Lash Procedure Part 1, Fueling the Fire Bracket Race & Street-Strip Fuel Delivery Systems Part 2, Fueling the Fire Bracket Race & Street-Strip Fuel Delivery Systems Part 1. We have had very good feedback on this particular additive. New points, coils, plug wires and boots. There is like no resistance while turning the air screws. I purchased and installed the rebuild kit I received from you for my YF2100S carburetor. 85. r/MechanicAdvice. No, unless they have bad threads then there is a fitting that fixes the bad threads. Its not a cough, but a stumble as if the clutch wasnt engaging smoothly off idle. Add and subtract then bench test the pump action. and close the primaries back to where they need to be.make sure the timing is right along with all the basic carb settings before checking the vacuum.it will probably drive ya nuts til you get it calmed down but keep trying. Checked the idle mixture screws and idle screw, car idles perfectly. Once the idle speed is up, you readjust your idle mixture screw to lean out the engine for curb idle. There are three main components of the accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. Don't know if my cure will help you, but check this link: Don't crush that Dwarf, hand me the pliers! Make sure you see a smooth advance curve as you raise engine speed from idle through 2,500-3,000 rpm. Hopefully you'll see a little tube, covered by a rubber plug. The Fora platform includes forum software by XenForo. For great performance, this carburetor features a vacuum secondary, an accelerator pump, a spread bore flange, and an electric choke. Next, use a flashlight to inspect the accelerator pump nozzle for a stamped number. Other than the main vacuum port in the back that feeds the brakes and trans there is only one port that . If you have the MoCo svc. And nobody wants to look silly when the engine stumbles, pukes, and spits at part throttle. Not a problem with the squirter. goldduster318. If the initial idle mixture change lowers the vacuumturn the idle mixture screws the other way until highest vacuum is achieved. By chance if this carburetor was transplanted before this all started then the problem may be the carburetor main jet is too big. When I raced KT100, they would never idle. 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. Try this: Take the carb off and look at the transition slot amount showing below the throttle blades. This isnt our expertise but some ideas are coil, old spark plugs, etc. Remember the drop can be anything as long as it lets the needle drop down, but not so far that the needle gets cocked to one side, or falls out. Turning this screw clockwise will rich the mixture and worsen the bog. 4-5 lbs should do it. PLEASE SEND HELP! See number 42 in the illustration. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. 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. This reduced vacuum requires more throttle opening to feed sufficient air to the engine since there is less of a differential between manifold vacuum and atmospheric pressure. The low-speed was set way too rich to idle. Check the viton tip for any signs of scaring. If any pressure was put on the needle when adjusting the float, then the needle may be damaged not allowing it to open. Carter YF 1 Barrel Carburetor Troubleshooting. Install new squirters (comes stock with .035" you want the bigger .043" squirters) 2.) How do you adjust this stumble? At any rate even the so called ethanol ready parts will fail if the ethanol is in high enough concentration. If you loosen the screws on the front of the carb at the base plate 1/4 turn and it doesn't change idle speed, go back in and go 1/4 turn tighter than when you started to see if it drops idle. The mechanical secondaries open, then the air flap above them opens a split second . I am looking to purchase a Carter rebuild kitPK105. 2023 HOLLEY PERFORMANCE PRODUCTS, INC. ALL RIGHTS RESERVED. This can happen when putting pressure on it when adjusting the float. The overall objective is to deliver the right amount of fuel. Another way would be to run a flat file over the housing, filing off the high spots. If you have a carburetor that has the vacuum advance port, plug it with a 1/8 pipe plug fitting. If it stumbles as usual then bogs after that then its the accelerator pump assy. 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). It may not display this or other websites correctly. JavaScript is disabled. Could it be running lean and causing it to stumble a bit off idle? Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect. Test the main discharge to make sure it is sealing when not in use. Seat the check ball using a brass drift punch and tap lightly.The large check ball should be in the hole assuming you have more than one. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! The single plane intake sees the cam overlap as a giant vacuum leak. Gas could be coming in the bowl around the seat. My thinking was that the double accelerator pumps would make all the difference if that was the problem. Jun 17, 2014. no i didnt make any changes to the holley as it was borrowed. You can learn how to do this here: https://www.carburetor-blog.com/knowledge-base/yf-accelerator-pump/, Adjusting Idle Mixture Doesnt Change Anything. Test the fuel pump pressure. odd that she just got serviced and they supposedly adjusted the clutch then. Problem now is I can't rev it past 2-3k rpm. Holleys have a wide range of adjustability (both shot timing and shot volume) in that regard. Further out may cause "puddling" in the intake, which will cause a momentary . Air:200. Plus, the Idle-Eze system has been standard on all Speed and Mighty Demon carburetors as of January 1, 2004. Then swapped a 750 vac . Usually a backfire through the carburetor is a sign of being too lean. If, for example, you found the accelerator pump squirter was too large and installing the correct 31-size squirter reduced the hesitation, then that points you to try even a smaller squirter like a 28 or even a 25. Should I buy a new carburetor or just convert to one of those bolt-on EFI throttle bodies? After each change, start the engine and check the throttle response. Notify me of follow-up comments by email. JavaScript is disabled. Float level was close, but float drop was way off. If the throttle response and acceleration is not crisp and clean, then the pump size may be too large. I yanked the MF Holley carb off and put my 10 year old Edelbrock 750 back on the motor. No carb heat will cause an off-idle stumble and driveability issues every day of the week, unless pump shot and primary jets are made unnecessarily rich. Now evaluate that change. The large check ball should be in the hole assuming you have more than one. The float drop should allow the needle to drop down enough to let fuel in. Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect. Thanks. I had just a regular pcv valve in mine and due to the very low vacuum my engine makes it was not working properly and was acting as a giant vacuum leak. Did you replace the fuel filter(s). Luckily a simple few turns should fix the problem. If the float isnt dropping, then the needle will not be pulled out of the seat and the float bowl will not fill up. Remove the idle tube and make sure it is clear. Fuel is dribbling out of the main discharge at idle. I see a spacer is optional on some models. Heat up some water and dip the float into the water. Get a wideband so you dont have to guess who bad off your tune is. Light throttle stumble, Holley carb. 1 position for idle speeds below 900 rpm and suggests moving to the No. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. "For those that will fight for itFREEDOM has a flavor the protected shall never know.". Make sure you installed the gasket under the seat. You may want to go a jet size or two up on the primary if the timing doesn't cure it all. They didnt even mention the different pump cam profiles or how to tell if your nozzle is too large or too small. The metering rod fits too loose in the main jet. Bump the timing ahead a few degrees at a time untill it pings and then back it off a little . sec. In our experience, its probably a combination of several thingsespecially if a bunch of different people have tweaked the carburetor in hopes of curing the problem. Timing at idle should not be in the 30's. Get it down to the low 20's with a limiter plate for the vacuum advance. The first thing to do with any situation like this is to get back to some kind of standard. Your accelerator pump isn't working. Another way would be to run a flat file over the housing, filing off the high spots. Same with wires. After reading, I noticed the OP says he has the XE294HR. hesitation during light throttle acceleration750 holley. Short summary: Stumble off idle under hard acceleration. With the exception of a vacuum leak, the idle is affected by the throttle valve being open. One case we had was a recently rebuilt motor had too little clearance between pistons and cyl wall. They should be burning tan or light brown. Idle Doesnt Kick Down When Coming to a Stop. JavaScript is disabled. Doha. A forum community dedicated to hot rod owners and enthusiasts. The Doug Roe book on Rochester carburetors is helpful in nomenclature. Just wipe until you dont get any black on the towel. 12. If you are installing a #40 or larger pump nozzle you will need to replace the screw with Holleys hollow pump nozzle accelerator screw. Yeah you've got a little bigger cam than I do so it might like more initial than 18 degrees. . 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 linkage should move and squirt a small amount of fuel with the lightest touch of the linkage. Test the fuel pump to make sure it isnt too low. Obviously the carburetor isnt getting gas. I've adjusted the idle mixture screws for max vacuum at idle. 3 days ago. Wipe the needle viton tip off with mineral spirits. Edited by EagleFreek - Jan/02/2010 at 8:31pm. My carb is on a '66 Impala. -rebuilt carb. Use a 0.015 feeler gauge to make sure the adjustment is correct. I also had a stumble. It should be about 4 lbs. Thats what causes the bogging and poor throttle response. Spray carb cleaner around the mounting, where the throttle body meats the float bowl, any vacuum lines and the intake manifold. Check the float drop. Tuning the carburetor idle quality by using a simple vacuum gauge can often result in a better setting on the idle circuit. I agree with Tom. later, KrustyTC. The Holley accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. You can try wiping off the viton tip with mineral spirits. Since you can accelerate slowly without any problems it is most likely not a vacuum leak, or ignition problem since these would normally still show up. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. If you would like to change your settings or withdraw consent at any time, the link to do so is in our privacy policy accessible from our home page.. When I give it throttle, it kinda makes a sucking air noise and stumbles. When the temps change you have to change your jetting although you can easily take away that bog (rich) by leaning out the air screw. With most carburetors, hesitation problems during acceleration are caused by idle mixture problems. For the YF probably around 4 lbs. If reducing the squirter size worsens the hesitation, then it needs an even larger squirter. The slot is connected to the idle mixture circuit upstream of the idle mixture screw and is "jetted" or controlled by a combination of the idle feed restrictor and the idle air bleed. 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). fuel has to atomize and some heat can be beneficial in colder climates. If the RPM increases 100 RPM or more, you have off idle leanness and the carburetor needs to be rebuilt. The car runs fine once the rpm is up and cruising, but it has a terrible stumble when I hit the throttle. Keep in mind that the idle screw opens the throttle valve, which speeds up the RPM. Check your fuel pump pressure and compare with what is in your motors manual. Make sure that it is clean and clear. Big Cam BluesSo why doesn't this circuit work on an engine with a big cam? Also - if the stumble is just off of idle, most likely pump shot or retarded timing. a cold intake, especially this time of year, can create a stumble. Heat up water just prior to boiling and immerse the float. Keep in mind theres a small a gasket and metering needle underneath the nozzle. Manage Settings For the YF probably around 4 lbs.The needle in the needle and seat may be damaged. First, locate the idle mixture screw. Do Not Sell or Share My Personal Information. Assuming the electrical system is working correctly then you either have a vacuum leak, or not getting enough fuel. We just need to run you through eliminating the problem area. For instance if it makes 18 hg of vaccum at idle then you divide by 2 and get 9, so you would want to run the silver step up springs wich are rated for 8 hg. 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. Leaking around the seat. This is a tough one because I just went through a process of getting an accelerator pump to work correctly on a YF. In fact I'm sure we do. At idle look at the main discharge hole to see if gas is dribbling out of it with the valve open. 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. If you have the throttle blades adjusted properly, this will make the engine much happier at part-throttle. I got a service manual and am learning to do most of my work myself. We transferred the new Edelbrock intake and carb to the new engine. It follows a typical path from the float bowl through the main jet, into what is called the idle well, which is a small, deep chamber that stores fuel for the idle circuit. Come join the discussion about performance, modifications, troubleshooting, builds, maintenance, classifieds and more! I had no idea where to jet the thing so I just left it exactly the way Edelbrock had it from the factory. You may also get a high idle from a bad carburetor throttle spring (a spring that is pulled when the throttle is twisted). My 2100 carb wants to stumble/die just as I leave idle. Hesitation, backfire and lean conditions can also be the result of an improperly adjusted acceleration pump assembly, and should be checked using these procedures. Non Carb stuff. Also the float should be aligned in the middle. You Connect a vacuum gauge to a manifold vacuum source . Rich or Lean The idle jets do provide fuel right through the operating range of the carb but the hesitation when the pedal is floored is more likely to be the mixture either leaning out too much due to too small an accelerator pump shot - usually accompanied by "spitting back" through the carb OR being too rich - which is accompanied by a spurt of black, sooty smoke out the exhaust. Continue with Recommended Cookies. And that is measured at wide open throttle using a feeler gauge. Mar 18, 2010. ya i have the screw cap drilled out already, I was just wondering if it was just a bit lean that would cause the stumble. i preferred a .025" squirter with tubes and a white 218 pump cam when i was running 6paks. Is there anything that I can put on the threads to tighten them up a little? Heat the housing with some pressure from a vise. Well, I am at a total loss. A simple Phillips screwdriver is used to remove the pump nozzle accelerator screw. Join. This clearance allows for maximum velocity of idle air past the idle ports. May 13, 2014 Start from 2 turns out. A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. To bring the curb idle back to the ideal spot of uncovering about 0.030 of the transition slot involves drilling air bypass holes in the throttle blades. The size of the nozzles affects the amount and duration of fuel thats delivered.

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