This can happen when putting pressure on it when adjusting the float. Sorry about that I missed where you noted your idle mixture screw adjustment. Lightly seat the mixture screw, then 2 turns out. though which is a much different animal than an Eddy. Consult your repair manual, if necessary. The throttle valve should be closed. The first result of a long-duration camshaft with lots of overlap is drastically reduced idle vacuum. And, you probably you dont even need a new carburetor. Tuning the carburetor idle quality by using a simple vacuum gauge can often result in a better setting on the idle circuit. Bike stumbles at idle to 1/4 throttle. For a better experience, please enable JavaScript in your browser before proceeding. Thanks. Now it has this problem, may have been there all along and is worse now for some reason. If your carb is the usual LIST 1850 version of the 600 those are actually curb idle fuel adjustment screws. Before moving any further, make sure the cam is set to . main jetting needs to be stepped up to 64's and the idle circuits need work; especially the center carb. . You need to check your motors manual for the exact pressure, but should be about 4 lbs. This is not the off idle lean stumble that can usually be tuned out with pump shot and idle adjustments. Heat the housing with some pressure from a vise. Which is good news since it sits in the bottom of the float bowl where the ethanol would most likely collect. Once they get too heavy, they will start to sink and let too much fuel in. secondary on it. We and our partners use cookies to Store and/or access information on a device. 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. To balance the idle mixture. Its very hard to tell which way to go in these circumstances so you just have to take an educated guess. I am looking to purchase a Carter rebuild kit. Add and subtract then bench test the pump action. Whilst following your adjustment instructions and when carrying out the metering rod adjustment, Can you tell me if I should disconnect the link pump connector first. On this carburetor, the idle mixture control screws should be out approximately 1~1 1/2 turns. I agree to receive emails from RacingJunk.com. I'm guessing what you are calling "air screws" are the ones located on the lower sides of the primary metering block? Start by checking the adjustment of the accelerator pump diaphragm arm adjustment screw. If the RPM smooths out, then you found your leak. Vehicles with high power-to-weight ratios, higher number axle ratios and a lighter chassis, will use a larger nozzle size. Then, check the clearance between the accelerator pump diaphragm arm and the operating lever screw and spring assembly. Do you know what your vacuum readings are in park and in gear at idle? 101. Right now while its in park i get 17-20 inches. I will get some vacuum readings in gear tonight and post them. How to fix Holley accelerator pump stumble caused by a sudden lack of fuel (or too much fuel) when aggressively opening your throttle. JavaScript is disabled. The metering rod does not fit tight. No matter how slowly I let out the clutch I still get the stumbling. hesitation during light throttle acceleration750 holley. Test the fuel pump pressure. These sometimes become warped and need to be made flat again. The off idle is not even close to the Holley. Im surprised he forgot to mention the power valve. most likely, cause it wasn't doing it before! Heads are stock 429 PI. Adjusted float level to 7/16" and float drop to 1" per specs in the manual. I also had a stumble. Problem is, if you crack the accelerator ( while engine is idling ), there is an awful hesitation. Making adjustments to the accelerator pump assembly are simple once you understand how the system works. you might have a hole in the accelerator pump diaphram. 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. Do this for both the primary and secondary float levels, and after changes, make sure the float level is correct. Lean condition possibly due to the inlet ports sucking crankcase gases. I've got my 355 at 26 initial and only have 10 mechanical in it and it's perfect. A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. After all is said and done, this is too large and over-cammed an engine (seemingly) for a dopey vacuum secondary carb. They have a pretty cool website with a lot of neat info on there. Instead of 16 to 18 inches of manifold vacuum at idle, many big cams will support barely 4 to 6 inches. You dont need to drill throttle plates. See number 42 in the illustration. 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. To narrow it down, tap the roll pin out of the accelerator pump lever by using a small pin punch or a small finish nail. Next, check the spark plug wires. Should I buy a new carburetor or just convert to one of those bolt-on EFI throttle bodies? 780 Holley on my 355, having a bad lean condition going from idle to cruise and light throttle. Check for vacuum leaks. Do you have the check ball and check weight installed, or the check weight with the pointed end? Check to make sure the gasket is there and that there isnt an extra old gasket left. 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. Instead of 16 to 18 inches of manifold vacuum at idle, many . 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. Sooty or black spark plugs. 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. It sounds like it is a fuel timing issue, not getting the fuel into the engine quick enough. Manage Settings There should be no gaps and the gauge should have a little tension on it when you pull it out. So Grant came up with an elegant solution he calls the Idle-Eze system. Blow out and re-try.Gas could be coming in the bowl around the seat. Heat up water just prior to boiling and immerse the float. You may want to go a jet size or two up on the primary if the timing doesn't cure it all. Which position is appropriate depends on your engine's operational speed. Ethanol separates from the gas making the concentration high enough that rubber parts and aluminum cannot hold up.One solution is to useEthanol Defensein your gas. I have been trying to get it working again for about 2 . Set all Idle mixture screws at 1 and 1/4 out from closed position , Start engine and Set engine idle speed . Hesitation off Idle. Do I need them or should I remove? Still have the same problem. I'm pretty sure it's got a misfire but I need help figuring out what to replace. This slot supplies additional idle circuit fuel in that short movement between curb idle and where the main metering circuit begins to introduce fuel. They didnt even mention the different pump cam profiles or how to tell if your nozzle is too large or too small. This article leaves out a bunch of detail. Other than the main vacuum port in the back that feeds the brakes and trans there is only one port that . This vacuum port. Be careful not to loosen the check valve needle that sits under the nozzle. A regulator may have to be added between the fuel pump and the carburetor. The passage is small and can plug easily. Continue with Recommended Cookies. 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. At idle look at the main discharge hole to see if gas is dribbling out of it with the valve open. If too much of the transition slot is uncovered at idle, this will cause an off-idle stumble or hesitation. Only runs when the choke valve is wide open. The black plugs suggest flooding, or too rich. Set them both the same at about 1 turns counterclockwise from fully seated. Learn how your comment data is processed. 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. Heat up some water just prior to boiling, immerse the float, any bubble indicates a leak. Back it down until it looks like a perfect square. Most people experiencing hesitation think, "put in bigger jets" right off the bat. http://www.nastyz28.com/forum/showthread.php?t=34200. 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. Hi guys, I finaly fixed all (hopefully!) If the engine seems to have an off-idle stumble, changing the size of the . JavaScript is disabled. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. Check the fast idle. Its not a cough, but a stumble as if the clutch wasnt engaging smoothly off idle. Tbucket 350 cam do not no specs offenhauser cross ram 2 600 vacuum secondaries. This carb is on a 460 in a 77 f150 4wd manual trans truck. Look in our YF carburetor manual and go over the metering rod adjustment. Float level set to:10mm. It is mounted on a 1946 Chevy truck with an in-line 6. Jun 17, 2014. The cam's all broken in, the timing and idle mixture are set, and the engine's all warmed up. Check for any cracks in the bowl top.Check the floats for leaks. This assembly delivers an initial shot of fuel in the right amount, and duration, to provide crisp throttle response right off idle. I see a spacer is optional on some models. The problem is, when I take off from a stop . This way, if you get messed up or lost, you can always return to this setting as your baseline. The 1st thing to do is remove the carburetor from the engine. Choke not needed from cold starts. Heat the housing with some pressure from a vise. Part throttle hesitation (going from light acceleration) 3.) Rpm's go up and down, car shakes at idle, and it has lack of acceleration/power. Check your float level. Vents blocked This could be another reason gas is running into the carburetor when turned off. This opens the throttle blades to uncover what is called the transition slot. Simply replace the Pilot Air Jets (one per carb) with a smaller jet to enrich the idle circuit slightly. A forum community dedicated to hot rod owners and enthusiasts. But by doing so, you're now using fuel supplied by the transition slot. You shouldnt be able to blow through (using about 5 lbs).Run thin wire through all of the small passages. Robert recommends a replacement jet - size #98. The idle screws turned full in is usually a sign of an internal leak. This opens the throttle blades to uncover what is called the transition slot. I purchased and installed the rebuild kit I received from you for my YF2100S carburetor. It's a big day. My suggestion is make sure you have a proper pcv valve, then advance initial timing, try larger squirter in that order. #1 thing to look at is the ignition. Check the viton tip for any signs of scaring. New fuel pumps are especially suspect. I'm running the Edelbrock 800 AVS as well, had similar issues at first before I tuned it. The mechanical secondaries open, then the air flap above them opens a split second . 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. 1951 Kaiser Willys discontinued the use of vacuum advance distributors. Usually a backfire through the carburetor is a sign of being too lean. The fast idle opens the throttle valve so that more air is used. (3) Check float needle and seat for proper seal. 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. Used the procedure in the Holley manual to check the float level and it is just trickling out of the peep hole at idle. I put one in for a 427 corvette motor and it runs like a different engine. This can be fixed by doing a rough adjustment. Make sure the choke valve is wide open when the engine is warmed up. Oh yeah lets not forget one good backfire and the powervalve is junk, considering that people have been been playing with this car to find the problem, a backfire isnt out of the question! 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. Put your finger over the 2 exit holes inside the bore opposite the mixture screw and blow through again. When I give it throttle, it kinda makes a sucking air noise and stumbles. Engine setup is a 72 block zero deck kb flat top bottom end. You've finally installed that lumpy cam in your big-block street-stormer, and you're ready for the testdrive. 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. 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. 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. if this just started , I would check out the accelerator pump. Check the floats for leaks. Not sure , but tried several times to set the 4 corner screws with very little positive results. It may have been changed to a larger one, which is often the wrong move. In fact I'm sure we do. The pump arm should move down a bit when the feeler gauge blade is inserted. Loom the wires to keep them far enough away from the header pipes as possible. You must log in or register to reply here. It should be about 4 lbs. Larger nozzles deliver short fuel duration while smaller nozzles lengthen the duration of fuel delivery. Float level was close, but float drop was way off. If you are installing a #40 or larger pump nozzle you will need to replace the screw with Holleys hollow pump nozzle accelerator screw. My question is are you sure your vacuum readings are right? If the intake manifold/head surfaces are not perfectly square and parallel or if the intake gaskets are not properly fitted to cover the ports on the interior side of the manifold/head interface, this can happen. I have 10.5:1 or so compression and AFR 195 heads. Ask me how I know. Product Description. , I feel I'm lost with sooooo many variables to think about! Come join the discussion about restoration, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more!

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