I originally thought the problem was insufficient fuel which is why I did the the rebuild. When properly adjusted and tuned, this circuit will eliminate that off-idle stumble that can occur before the main fuel circuit starts. Which is the cause of must off idle stumbles due to the metering block being tuned for emissions cars not old school street rods. Seems to get a little better after the engine is fully warmed up. i wouldn't run a completely blocked heat crossover. As most have been saying; there is an off-idle stumble that's much worse when the car is cold. For starters make sure the carb is box stock. It returns excess pump discharge to the float bowl. 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. Regardless of how you approach the repair of this problem, the key is the proper relationship of the throttle blades to the idle transition slot. What do you have for compression? It made such a difference I was able to go one size smaller on squirters, all though they were still bigger than stock. Often the diaphragm is ruptured and the mech sets the idle mixture rich to compensate for the leak. Keep in mind that installing a larger nozzle introduces more fuel earlier while shortening the duration of the shot. Now he serves as a regular contributor to OnAllCylinders. After reading, I noticed the OP says he has the XE294HR. Some of our partners may process your data as a part of their legitimate business interest without asking for consent. We have had very good feedback on this particular additive.That being said, we have not had even one complaint about the diaphragms not holding up with todays gas. Terrible stumble off the hit . The closest fraction is 9/64. Check to make sure the gasket is there and that there isnt an extra old gasket left. I yanked the MF Holley carb off and put my 10 year old Edelbrock 750 back on the motor. You shouldnt be able to blow through (using about 5 lbs).Run thin wire through all of the small passages. This tells me that when the choke valve is closed there is too much gas being pulled into the engine. See this page to learn about the accelerator pump diaphragm. These sometimes become warped and need to be made flat again. This time it would idle nicely at about 900 rpm. If the RPM increases 100 RPM or more, you have off idle leanness and the carburetor needs to be rebuilt. Jets are probably not the problem unless they are a lot oversized. You must check this with the vacuum advance disconnected. Manually raise the float to see if you feel any catching. Now with the linkage eliminated pump the throttle. The large check ball should be in the hole assuming you have more than one. Your email address will not be published. For the YF probably around 4 lbs. This can happen when putting pressure on it when adjusting the float. Fuel Pressure is 6 psi with a regulator and the . VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. How do you adjust this stumble? -manifold distributor advance set at 8 degrees BTDC. Big Cam BluesSo why doesn't this circuit work on an engine with a big cam? New fuel pumps are especially suspect. Do not plug it off. For a better experience, please enable JavaScript in your browser before proceeding. Start from 2 turns out. Keep in mind I'm using a Holley style carb. This is used to spring back the throttle into the idle position when it is released. No matter how slowly I let out the clutch I still get the stumbling. 101. Once they get too heavy, they will start to sink and let too much fuel in. For a better experience, please enable JavaScript in your browser before proceeding. Idle Eze throttle plate assm., 850 mech. 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. 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. Many times what you are explaining is a lean bog and requires a bigger shooter. Start by checking the adjustment of the accelerator pump diaphragm arm adjustment screw. Make sure the choke valve is wide open when the engine is warmed up. I agree with Tom. The off idle is not even close to the Holley. Post rebuild, and with no noticeable change in symptoms, I pulled a plug (all new) and found them to be black with soot buildup. most likely, cause it wasn't doing it before! Easy to experiment. Any bubbles means its leaking. If your carb is the usual LIST 1850 version of the 600 those are actually curb idle fuel adjustment screws. 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. This slot is exposed to manifold vacuum as soon as the throttle is opened. Are the materials in this kit compatible with ethanol-blended fuels? Does it still jerk? Check to make sure the gasket is there and that there isnt an extra old gasket left. Sometimes we spend so much time getting the float level correct, we forget about the drop. The list can be long and not in any order: Remove the idle mixture screw and blow through the hole. 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. That's when they ran their best on the track. Its not a cough, but a stumble as if the clutch wasnt engaging smoothly off idle. They have a pretty cool website with a lot of neat info on there. Dirt may have entered the carburetor after it was rebuilt. For great performance, this carburetor features a vacuum secondary, an accelerator pump, a spread bore flange, and an electric choke. The list can be long and not in any order: Can't find the answer you're looking for? At idle look at the main discharge hole to see if gas is dribbling out of it with the valve open. Helps make tuning very easy. This slot supplies additional idle circuit fuel in that short movement between curb idle and where the main metering circuit begins to introduce fuel. Place the housing between 2 flat metal stocks. Check the throttle valve now. For more information, visit www.holley.com. Idle-Eze throttle plate assm., 650/750-cfm, vac. Follow the main jet passageway to make sure it is clear. Sooty or black muffler end pipes. 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. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. High vacuum could mean an overly advanced distributor. Off-Idle surging is a common occurrence after installing a carburetor. Disconnect the link that connects the throttle shaft to the accelerator diaphragm arm. They tend to absorb over time (years). Required fields are marked *. 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. Dan Sanchez Then drop the idle speed to where you want it to idle in RPM and . In my opinion 77 primary is rich for a mild 355. A forum community dedicated to hot rod owners and enthusiasts. 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. Wait until the engine returns to the previous idle. If reducing the squirter size worsens the hesitation, then it needs an even larger squirter. This is indicative of a problem in the carburetor. Gently move the float up and down to see if you can feel any catching. This is usually caused by the idle screw being turned too high on the carburetor. Get a wideband so you dont have to guess who bad off your tune is. I am looking to purchase a Carter rebuild kitPK105. Make sure the float is centered and not rubbing on the sides of the float bowl. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. The carburetor is a Holley 750 with vacuum secondary. Next, check the spark plug wires. Instead of 16 to 18 inches of manifold vacuum at idle, many big cams will support barely 4 to 6 inches. 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. Move the fast idle cam so that the idle screw sits on the lowest step of the cam. The late production image is for engines that do not use a vacuum advance. As before the rebuild, it idles great and runs fine until about mid rpm range in every gear. Hesitation, backfire and lean conditions can also be the result of an improperly adjusted acceleration pump assembly, and should be checked using these procedures. Stay up to date with the latest releases, events, promotions and more. It gets about 10 mpg set up like this. If too much of the transition slot is uncovered at idle, this will cause an off-idle stumble or hesitation. This should not be happening. Bike stumbles at idle to 1/4 throttle. Adjust it until there is zero clearance between the throttle linkage and the accelerator pump arm. I believe we have the same cam. I'm running a 1411 carb on top of a Performer intake and stock internals. Your email address will not be published. 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. This is normal for the Carter YF & YFA. The goal is to deliver the right amount of fuel at the right time. . Ask me how I know. 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. The single plane intake sees the cam overlap as a giant vacuum leak. Once they get too heavy, they will start to sink and let too much fuel in. "For those that will fight for itFREEDOM has a flavor the protected shall never know.". Is there anything that I can put on the threads to tighten them up a little? They also left out the transition circuit. '75 and '77 models use stock Keihin Pilot Air Jets - size #110. Check for any cracks, or perhaps the old gasket is still underneath. Besides all this I have a choke problem. Come join the discussion about performance, modifications, classifieds, troubleshooting, maintenance, and more! Luckily a simple few turns should fix the problem. The metering rod fits too loose in the main jet. Typically, heavier vehicles with low numbered axle ratios (like 3.23:1) will use a smaller nozzle. Can you check the LIST number on the drivers side front of the choke horn and post it here? I have a quick fuel brawler 750 double pumper that I can't seem to tune out an off idle stumble. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. Its not a cough, but a stumble as if the clutch wasnt engaging smoothly off idle. 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.. 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 would Say a 70 primary is more in the ballpark. hesitation during light throttle acceleration750 holley. 4-5 lbs should do it. Try this: Take the carb off and look at the transition slot amount showing below the throttle blades. Only runs when the choke valve is wide open. Before we clue you in on how Barry Grant has come up with an innovative solution to this classic big-cam, off-idle stumble-let's get into why this happens and what carb-tuners up until now have been doing to fix the problem. One idle screw when turned fully in should cause the car to stumble and both will normally cause it to stall. Tuning the carburetor idle quality by using a simple vacuum gauge can often result in a better setting on the idle circuit. A non vented cap will cause a suction. Rpm's go up and down, car shakes at idle, and it has lack of acceleration/power. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. It may have been changed to a larger one, which is often the wrong move. 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. Come join the discussion about restoration, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! Be sure your running the proper fuel pressure. Page 1 of 3 1 2 3 Next . You must log in or register to reply here. Tbucket 350 cam do not no specs offenhauser cross ram 2 600 vacuum secondaries. For a better experience, please enable JavaScript in your browser before proceeding. . We have had very good feedback on this particular additive. Idle Doesnt Kick Down When Coming to a Stop. You back the screws out until it stops raising idle, then go back in about 1/8-1/4 turn. fuel has to atomize and some heat can be beneficial in colder climates. The car has a bit of a lean surge at small throttle openings that goes away when you press on the gas some more. I got a service manual and am learning to do most of my work myself. Float level was close, but float drop was way off. Make sure you installed the gasket under the seat. Usually a backfire through the carburetor is a sign of being too lean. You're running rich man. For a better experience, please enable JavaScript in your browser before proceeding. Look at your plugs to see how they are burning. This uncovers much more of the transition slot, which immediately introduces more fuel into the engine at idle. One or more of these are out of wack. If it all looks good, then take the top off and check the Accelerator pump diaphragm to see if it is put together correctly. VerticalScope Inc., 111 Peter Street, Suite 600, Toronto, Ontario, M5V 2H1, Canada. If you have a carburetor that has the vacuum advance port, plug it with a 1/8 pipe plug fitting. Leaking around the seat. Test the main discharge to make sure it is sealing when not in use. Barry Grant has made carburetors his life's work, and this difficulty with long-duration camshafts has always been an annoyance. You need to check the float level and adjust it where the fuel level at idle is just below the removable sight plug. Weve seen this work very well. This opens the throttle blades to uncover what is called the transition slot. Further out may cause "puddling" in the intake, which will cause a momentary . Run thin wire down the hole to clear out any ethanol residue. The answer is amazingly simple. 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. Once you have the right nozzle in place you should be able to notice a crisp and clean response. WOT hesitation (flooring it from a roll or dead stop) . Short summary: Stumble off idle under hard acceleration. Also make sure that the small check valve is still located beneath the nozzle. 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. Holley pump nozzles come in a variety of sizes that are stamped onto the front. Turning this screw clockwise will rich the mixture and worsen the bog. Start by increasing the fuel nozzle size up by three sizes. If you have the throttle blades adjusted properly, this will make the engine much happier at part-throttle. It seems to have a stumble when you mash the gas. You drop it in gear, tip in the throttle, and the engine dies. Atomization Abounds. Fuel is dribbling out of the main discharge at idle. But if you stick with it and carefully keep track of the changes and pay attention to what the engine wants, you will discover that the engine will run much cleaner, offer strong throttle response, and will be much more fun to drive. Light throttle stumble, Holley carb. Jun 11, 2009. Make sure you have a good in line filter. You then tweek the idle rpm speed with the ignition base timing and the air flow thru the PCV valve internal orifice at idle to get more or less idle air flow and idle rpm speed. Idle-Eze throttle plate assm., 650/750-cfm, mech. Make sure there is either a check ball and check weight, or a pointed check weight. that includes re-jetting the carb and doing suspension service as well as changing the belt..Basically anything that does not need a lot of special tools to do..Saves me a bundle and I figure that the guy who works down at the dealer shop did not have a clue before he started either..:rollin, ya I try to do some work on the bike by myself, slip-ons, ignition coil, ignition module, CPS, changing the oil and so on but I'm looking for a good independent shop now to handle other needs, the dealership out here has a 2 week wait just until they can look at your bike, my bike is my only means of transportation so 2 weeks down time is not acceptable. when riding shifting is smooth. The suction you cause will sometimes unclog a passage. Wadd2 those are the bushings I was referring to. JavaScript is disabled. cams XR294HR and it has .242/.248 at .050 duration. I actually use a small, broken drill bit that's just the right size. Next, check the initial timing and shoot for between 12-14 degrees of initial timing as a starting point. sec. 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. Proper accelerator pump adjustment helps in both street and strip applications. Engine setup is a 72 block zero deck kb flat top bottom end. 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). Check for any cracks in the bowl top.Check the floats for leaks. Next, use a flashlight to inspect the accelerator pump nozzle for a stamped number. Any leaks will bubble. Choke not needed from cold starts. We just need to run you through eliminating the problem area. 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. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. i preferred a .025" squirter with tubes and a white 218 pump cam when i was running 6paks. With the engine warmed up is the choke valve open completely? 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. The metering rod does not fit tight. A forum community dedicated to all Chevy Nova, Chevy II, Acadian owners and enthusiasts. easy to fix if you know how. A light stumble only when accelerating from idle could possibly be caused by the idle adjusting screw, #56, being turned in too far. The fast idle opens the throttle valve so that more air is used. With engine off, look down the carburetor. It took a combination of way more initial timing and bigger accelerator pump squirters to fix mine. 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 See number 42 in the illustration. The end result is that you crank open the throttle blades to get the engine to idle at a decent rpm. (Image/Holley). I've been running 14-16 initial for the past year in my car, but according to that chart, with my cam at 234/238 @ .050" I should be running 18-22 initial. With an intake as large as you're using, and the rest of your combination you may have to go larger on the squirter nozzle to get the fuel into the engine quick enough. Thats what causes the bogging and poor throttle response. New fuel pumps are especially suspect. The cam is 470 lift with 272 adv. Sluggish acceleration. Your email address will not be published. Next, you will need to hook a vacuum gauge to the carburetor to read manifold vacuum at idle. 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. Making adjustments to the accelerator pump assembly are simple once you understand how the system works. If you crack the accelerator from about 1200 rpm, there is no hesitation. 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. The passage is small and can plug easily. I guess I may just be used to having a mini starter though. Doha. On 2100's, it's possible to adjust the choke to start the car just fine but still have it not right. Idle BasicsAll carburetors come with a simple yet efficient idle circuit.

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