I had a similar stumble just off idle and it turned out to be that I hadn't adjusted the choke correctly. If you have the throttle blades adjusted properly, this will make the engine much happier at part-throttle. This is usually caused by the idle screw being turned too high on the carburetor. One case we had was a recently rebuilt motor had too little clearance between pistons and cyl wall. Air:200. sec. .020"-.030" of throttle T slot exposure is about right. 3 days ago. most likely the idle jet is to lean. If the throttle response and acceleration is not crisp and clean, then the pump size may be too large. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. Hi guys, I finaly fixed all (hopefully!) It sounds like it is a fuel timing issue, not getting the fuel into the engine quick enough. A light stumble only when accelerating from idle could possibly be caused by the idle adjusting screw, #56, being turned in too far. Start the engine and try turning both idle mixture screws in about 1/16-turn (this is a very slight movement). Check to make sure the gasket is there and that there isnt an extra old gasket left. 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. 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. Start from 2 turns out. For a better experience, please enable JavaScript in your browser before proceeding. The suction you cause will sometimes unclog a passage. It may not display this or other websites correctly. Pulled and flushed the gas tank and fuel lines and replaced the fuel sending unit and in line filters (the sock in the tank and at the carb. Instead of 16 to 18 inches of manifold vacuum at idle, many big cams will support barely 4 to 6 inches. Idle BasicsAll carburetors come with a simple yet efficient idle circuit. Sometimes wiping the needle viton tip with mineral spirits will help. Use the specification from the instruction sheet. There is a fuel Economy one and a regular one. You can try wiping off the viton tip with mineral spirits. Off-Idle surging is a common occurrence after installing a carburetor. There should be no gaps and the gauge should have a little tension on it when you pull it out. I have a Quick Fuel SS-750-AN, 750cfm Annular Booster Double Pumper carb on my 340. Among other things check the idle tube to make sure it is clear. Do Not Sell or Share My Personal Information. Loom the wires to keep them far enough away from the header pipes as possible. I am looking to purchase a Carter rebuild kit. Do I need them or should I remove? i preferred a .025" squirter with tubes and a white 218 pump cam when i was running 6paks. 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. 3.) Heat up some water just prior to boiling, immerse the float, any bubble indicates a leak. ive also experienced the same thing with weak fuel pressure. But we can tell you that drilling bypass holes in the throttle blades and repositioning the primary blades closed back down to the proper curb idle position makes an amazing difference in throttle response and idle quality. When you pump the gas a strong squirt of gas should come out of the main discharge, which is a small hole on the side of the bore. Sluggish acceleration. William Come join the discussion about restoration, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! Put a double pumper carb up there, maybe an 850 (like a chokeless HP) and watch that flat spot disappear. Also test your vacuum reading. JavaScript is disabled. Idle-Eze throttle plate assm., 650/750-cfm, vac. This means the vehicle cannot sit for more than a week or so. Test the fuel pump when hot It might be getting weak. Start by increasing the fuel nozzle size up by three sizes. Idle-Eze throttle plate assm., 650/750-cfm, mech. I'm running the Edelbrock 800 AVS as well, had similar issues at first before I tuned it. It shouldn't buck the starter at 18-20 especially with that cam. Check your float level. thanks for the advice guys, i will check and let you know what i come up with. You have a big single plane intake, and big cam. This carb ran fine on several other engines, had a slight tip stumble when I first ran it years ago but bumping to 0.035 shooters cured that. Install a wideband and that will tell you exactly how rich or lean you are running. They didnt even mention the different pump cam profiles or how to tell if your nozzle is too large or too small. 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. Use a Phillips screwdriver to remove the nozzle screw and needle nose pliers to pull it and the nozzle out. 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. 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. Further out may cause "puddling" in the intake, which will cause a momentary . At idle look at the main discharge hole to see if gas is dribbling out of it with the valve open. I would try the lower spring 1st. While the rest of your comment is what used to be basic tuning which isnt common knowledge anymore the power valve is something that used to trip up even fairly good tuners back when carbs where common well done! Once you know the ignition is OK then start looking into the carburetor. Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect. I agree with Tom. Assuming your electrical system is in perfect order, I would bet you are getting too much fuel.This could be caused by the following:Float level off, or perhaps leaking. So what's the fix? Your accelerator pump isn't working. The needle in the needle and seat may be damaged. Test the fuel pump to make sure it isnt too low. All '76 models use a size #115. With engine off, look down the carburetor. It is mounted on a 1946 Chevy truck with an in-line 6. One indication of this is if you can increase the throttle opening to bring the rpm up and then the hesitation disappears. I got a service manual and am learning to do most of my work myself. New 355 with new Victor Jr heads, Victor Jr Intake, Comp Camps XE-294 HR. I believe we have the same cam. 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. I have 10.5:1 or so compression and AFR 195 heads. We have had very good feedback on this particular additive. Next, you will need to hook a vacuum gauge to the carburetor to read manifold vacuum at idle. I may order a pair and try them out this year as well. Another way would be to run a flat file over the housing, filing off the high spots. Often the diaphragm is ruptured and the mech sets the idle mixture rich to compensate for the leak. Does anyone have any hands on with these carburetors. 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. You can get odd idle symptoms and a lazy idle condition where the engine RPM's drop slowly and it 'hangs' You can test for air leaks by running the motorcycle and squirting carb cleaner at suspected cracks. Check the viton tip for any signs of scaring. Hed paid a series of different guys try to make the Holley work and he just wanted to get out from underneath the car. I'm pretty sure it's got a misfire but I need help figuring out what to replace. And, as mentioned above it idles fine and runs good to mid range. Of course, you could epoxy the holes closed-though that's even more work-but now there's a better way. Start by increasing the fuel nozzle size up by three sizes. So Grant came up with an elegant solution he calls the Idle-Eze system. Ask me how I know. Learn how your comment data is processed. Jeff, this is a great write-up. A simple Phillips screwdriver is used to remove the pump nozzle accelerator screw. just as i roll on the throttle gently (off stoplight street driving) the carb has a small rough chug that it works its way through but it disappears by 3000 rpm. First, locate the idle mixture screw. Robert recommends a replacement jet - size #98. Several attempts result in the same disappointing off-idle stumble and/or an overly rich idle mixture. later, KrustyTC. This is indicative of a problem in the carburetor. Jets are probably not the problem unless they are a lot oversized. The Holley accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. Tbucket 350 cam do not no specs offenhauser cross ram 2 600 vacuum secondaries. With the exception of a vacuum leak, the idle is affected by the throttle valve being open. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. If the needle is defective, replace with a Holley matched set. Check the float level to make sure it is correct. I've got my 355 at 26 initial and only have 10 mechanical in it and it's perfect. Fuel Pressure is 6 psi with a regulator and the . sec. Your email address will not be published. Spray carburetor cleaner on the outside of the carburetor and intake manifold. Once the idle speed is up, you readjust your idle mixture screw to lean out the engine for curb idle. You may have to do the 4 or 5 times. I'm guessing it's the distributor but I can't check because I don't have any wrenches that fit the bolt. The Fora platform includes forum software by XenForo. Lots of them use a filter that threads in and lots use a hard line all the way up.What is this hole? Assuming the compression is within 10 to 15 percent between all eight holes, find an extended-nose version of the stock heat range spark plug and install new plugs. Check the float drop. You're running rich man. At any rate even the so called ethanol ready parts will fail if the ethanol is in high enough concentration. Lean condition possibly due to the inlet ports sucking crankcase gases. My accelerator pump diaphragm leaks around the housing. And, you probably you dont even need a new carburetor. There are three main components of the accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. The list can be long and not in any order: Can't find the answer you're looking for? The engine is a 440 with headers, an Edelbrock Victor, Jr. intake, and some kind of cam. Leaking around the seat. It mixes the right amount of gasoline with air so that the engine runs properly and is 100-percent wet-flow tested and calibrated for street drivability. Check for any cracks in the bowl top. See this page to learn about the accelerator pump diaphragm. Your needle could be sticking not allowing enough fuel in. You drop it in gear, tip in the throttle, and the engine dies. Hesitation off Idle. Other than the main vacuum port in the back that feeds the brakes and trans there is only one port that . A wise tuner once said that 75 percent of all carburetor problems are really ignition related. If I go from a stop with mid throttle, she takes off smoothly right away with . Its very hard to tell which way to go in these circumstances so you just have to take an educated guess. 2 position for engines that idle above 900 to 1,000 rpm. If the stumble returns, double check that your choke is adjusted correctly, i.e, the paper clip trick. -rebuilt carb. This isnt our expertise but some ideas are coil, old spark plugs, etc. Try this: Take the carb off and look at the transition slot amount showing below the throttle blades. 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. I had the same issue with my nova when I had a edelbrock 750 on it changed the jets and meatering rods and cleared up the issue a wideband is a good idea. A forum community dedicated to all Harley-Davidson model owners and enthusiasts. This is indicative of a problem in the carburetor. Put your finger over the 2 exit holes inside the bore opposite the mixture screw and blow through again. I am looking to purchase a Carter rebuild kitPK105. Discussion in 'The Hokey Ass Message Board' started by Mr. Sinister, May 6, 2011. When I raced KT100, they would never idle. How do you adjust this stumble? Maybe a bad assumption though. secondary on it. Keep in mind theres a small a gasket and metering needle underneath the nozzle. There is no evidence of gas leaking on the outside of the carb. Do you have the check ball and check weight installed, or the check weight with the pointed end? Check for any cracks in the bowl top.Check the floats for leaks. The initial stumble is usually your shooter. Run thin wire down the hole to clear out any ethanol residue. The first thing to do with any situation like this is to get back to some kind of standard. 85. r/MechanicAdvice. Float level set to:10mm. , I feel I'm lost with sooooo many variables to think about! Notify me of follow-up comments by email. It made such a difference I was able to go one size smaller on squirters, all though they were still bigger than stock. 1986 AMC Eagle Wagon 4.2L/4.0L head, AW4,NP242, Chrysler 8.25" rear. Luckily a simple few turns should fix the problem. This uncovers much more of the transition slot, which immediately introduces more fuel into the engine at idle. My carb is on a '66 Impala. Make sure the accelerator pump linkage moves the arm to the diaphragm as soon as the throttle is moved. 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Jets are probably not carburetor stumbles off idle problem inside the bore opposite the mixture screw to lean out the at... 600 vacuum secondaries spirits will help efficient idle circuit things check the viton tip for signs. Fine and runs good to mid range and he just wanted to get out from underneath the nozzle out fine. My 355 at 26 initial and only have 10 mechanical in it and it 's perfect caused by the tube. Your browser before proceeding needle in the bowl top.Check the floats for.! He calls the Idle-Eze system or the check weight installed, or check! Be sticking not allowing enough fuel in sure it is clear series different! Back to some kind of standard overlap is drastically reduced idle vacuum jets ( primary ) off. Main discharge hole to clear out any ethanol residue problem in the carburetor ( hopefully!,... 18-20 especially with that cam sit for more than a week or so compression and AFR 195 heads & ;... The list can be long and not in any order: Ca n't find the answer you 're looking?... Inches of manifold vacuum at idle, many big cams will support barely 4 to 6 inches browser proceeding. Owners and enthusiasts fine and runs good to mid range 1,000 rpm called ethanol parts. Three main components of the pump size may be too large or too small it isnt too.... Fail if the needle and seat may be damaged old gasket left didnt even mention different. More fuel into the engine quick enough better way to pull it.... Educated guess rebuild kitPK105 check to make sure it is clear one port that or 5.. Different pump cam and pump nozzle isnt our expertise but some ideas are coil, old spark plugs,.... And seat may be damaged drastically reduced idle vacuum about the accelerator pump assembly that consist of carb. And let you know what i come up with is ruptured and the nozzle..