-replaced accelerator pump twice. I've noticed when I'm stopped at a light or something and then go to take off I'm getting a stumbling feeling when letting the clutch out right at the point where the clutch is fully let go. Manage Settings Move the fast idle cam so that the idle screw sits on the lowest step of the cam. I've adjusted the idle mixture screws for max vacuum at idle. Are the carburetor kit parts ethanol ready? You are using an out of date browser. Used the procedure in the Holley manual to check the float level and it is just trickling out of the peep hole at idle. 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. Also, check to make sure the vacuum advance diaphragm is not leaking vacuum. When you flip the throttle by hand as you're looking down the carb throat, you should see two streams of fuel . Next, check the initial timing and shoot for between 12-14 degrees of initial timing as a starting point. You dont want to deliver too much fuel too soon, or to little fuel too late. Thats what causes the bogging and poor throttle response. For a better experience, please enable JavaScript in your browser before proceeding. Now he serves as a regular contributor to OnAllCylinders. This should not be happening. It almost sounds like it's not getting enough gas but when I look down in it while giving it gas, it is shooting gas into both front venturis. Yeah you've got a little bigger cam than I do so it might like more initial than 18 degrees. There is a fuel Economy one and a regular one. Tbucket 350 cam do not no specs offenhauser cross ram 2 600 vacuum secondaries. The Fora platform includes forum software by XenForo. 1 position for idle speeds below 900 rpm and suggests moving to the No. Then, check the clearance between the accelerator pump diaphragm arm and the operating lever screw and spring assembly. Start by increasing the fuel nozzle size up by three sizes. If you crack the accelerator from about 1200 rpm, there is no hesitation. I have disassembled the top of the carb and all appears to be in order. Gas could be coming in the bowl around the seat. JavaScript is disabled. 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. This means that the carburetor is flooding and when this happens the gas runs down the carburetor and out the 1st place it can, which is the throttle shaft.Some of the things to look for:Check your fuel pump pressure and compare with what is in your motors manual. Check the viton tip for any signs of scaring. It is built to restrict a certain amount of fuel, not to shut if off. A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. I am looking to purchase a Carter rebuild kitPK105. I had a similar problem with my 383 with Holley carb. If the RPM smooths out, then you found your leak. The Fora platform includes forum software by XenForo. Spray carburetor cleaner on the outside of the carburetor and intake manifold. Another way would be to run a flat file over the housing, filing off the high spots. 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. Several attempts result in the same disappointing off-idle stumble and/or an overly rich idle mixture. Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect. Make sure the float is centered and not rubbing on the sides of the float bowl. It's a big day. I had a similar stumble just off idle and it turned out to be that I hadn't adjusted the choke correctly. This is indicative of a problem in the carburetor. You can hit the throttle hard enough to pump fuel into the engine and launch with tires spinning and everything's great-but you can't seem to execute an easy, light-throttle leave from a stoplight.Arrrggghhh! Robert recommends a replacement jet - size #98. 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. See number 42 in the illustration. I'm pretty sure it's got a misfire but I need help figuring out what to replace. you might have a hole in the accelerator pump diaphram. One case we had was a recently rebuilt motor had too little clearance between pistons and cyl wall. Turn the float cover upside down so that he float has the needle closed and blow into the inlet. I would try the lower spring 1st. Too much cam, too big a diaphram maybe. They tend to absorb over time (years). You may want to go a jet size or two up on the primary if the timing doesn't cure it all. If it is, it can cause all sorts of problems. Terrible stumble off the hit . Increasing the idle jets in the metering block solves this issue. [ame]http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf[/ame]. 2023 HOLLEY PERFORMANCE PRODUCTS, INC. ALL RIGHTS RESERVED. 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 would Say a 70 primary is more in the ballpark. This can happen when putting pressure on it when adjusting the float. It has a good stream of gas coming from the accelerator pump. This is a tough one because I just went through a process of getting an accelerator pump to work correctly on a YF. Nothing aggressive, just pulling off from a stop, like . I understand that I can unsubscribe at any time. An example of data being processed may be a unique identifier stored in a cookie. Test the fuel pump when hot It might be getting weak. Besides all this I have a choke problem. duration. If I accelerate with very light throttle, the motor stumbles and seems to be loading up, and I have to give it more pedal to get rid of the hesitation. Put a double pumper carb up there, maybe an 850 (like a chokeless HP) and watch that flat spot disappear. You must log in or register to reply here. We often see where the adjustable spring is set incorrectly. 3 days ago. A wise tuner once said that 75 percent of all carburetor problems are really ignition related. Sooty or black muffler end pipes. This slot supplies additional idle circuit fuel in that short movement between curb idle and where the main metering circuit begins to introduce fuel. 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. Wadd2 those are the bushings I was referring to. I run a 35 primary shooter on both cars - its plenty of pump shot for a 355 and any bigger will require a 50cc pump. Stay up to date with the latest releases, events, promotions and more. Choke not needed from cold starts. If they are way off, thats good. Required fields are marked *. Ask me how I know. . Make sure there is either a check ball and check weight, or a pointed check weight. WOT hesitation (flooring it from a roll or dead stop) . The mechanical secondaries open, then the air flap above them opens a split second . The engine is a 440 with headers, an Edelbrock Victor, Jr. intake, and some kind of cam. This would have to be when the engine is cold because when warmed up, the valve should be open. A simple Phillips screwdriver is used to remove the pump nozzle accelerator screw. I guess I may just be used to having a mini starter though. Spray carburetor cleaner into the throat of the carburetor. Adjusted float level to 7/16" and float drop to 1" per specs in the manual. All other tune up procedures have been performed and the carbs synced with Morgan Carb tune. Non Carb stuff. Replaced the stock .035 . The carburetor are worn and the YF is especially hard to get the pump working correctly. For the YF probably around 4 lbs. Short summary: Stumble off idle under hard acceleration. As most have been saying; there is an off-idle stumble that's much worse when the car is cold. Your email address will not be published. Further adjustment is required but the problem is essentially solved. (Jets,Rods,Springs). Wipe until you dont get any black.Dirt may have gotten into the needle and seat. The answer is amazingly simple. I followed your advice and worked the ignition system. Light throttle stumble, Holley carb. Do not plug it off. Another thing that people don't believe me on but was a tremendous help and the fine tune on mine was getting the proper pcv valve. There is no evidence of gas leaking on the outside of the carb. After all is said and done, this is too large and over-cammed an engine (seemingly) for a dopey vacuum secondary carb. 1998 Chevy Z71 Full Size Pick-up Vortec 350. no, don't put anything on the threads. Tom Terrific or Terrible Tom, depending on the phase of the moon, passing cosmic rays or other factors not fully understood except by my wife. I actually use a small, broken drill bit that's just the right size. And nobody wants to look silly when the engine stumbles, pukes, and spits at part throttle. Take the carb off and look. Did you replace the fuel filter(s). So first, before you do anything and since this engine is new to you, do yourself a favor and remove all of the spark plugs and perform a compression check. Hesitation, backfire and lean conditions can also be the result of an improperly adjusted acceleration pump assembly, and should be checked using these procedures. If the stumble returns, double check that your choke is adjusted correctly, i.e, the paper clip trick. Beyond that however the engine starts to spit and sputter. Thanks. Remove the idle mixture screw and blow through the hole. Discussion in 'The Hokey Ass Message Board' started by Mr. Sinister, May 6, 2011. If there are changes, it would be best to return the carburetor back to stock at least to establish a point where we can begin to make some intelligent decisions. And, as mentioned above it idles fine and runs good to mid range. Could it be running lean and causing it to stumble a bit off idle? Be careful not to melt the metal. Atomization Abounds. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! Check for any cracks in the bowl top.Check the floats for leaks. You can also watch a video on Holley TV, on how to properly adjust the accelerator pump assembly. 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. Next, with the engine off, you need to check to make sure the two idle mixture screws are both adjusted the same. Luckily a simple few turns should fix the problem. Run thin wire down the hole to clear out any ethanol residue. 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. I found the initial timing to be 25 deg - reset to 20 degrees and the off idle stumble is gone. We transferred the new Edelbrock intake and carb to the new engine. Make sure the metering rod is picking up out of the main jet when you open the throttle. The Honda part number for this replacement jet is 99164-601-0980. 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