holley carb flat spot off idle
I have had engines go all the way up to a 9.5 power valve. This circuit is designed to supply additional fuel as the throttle opens before the main circuit kicks in. 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! The vacuum operated power enrichment system is controlled by a Power Valve that times the operation to your engine's specific needs. Regardless if you have a two- or four-corner idle adjustment on your QFT™ carb, start by setting all of the idle adjustment screws the same (1-1/4 turns from bottomed out in the metering block is a good place to start). You are actually 8 more than stock. Now that the new motor is in I know Im gonna have to jet up more. Holley has been the undisputed leader in fuel systems for over 100 years. Did you check/clean the filter already??? If it got worse with a 4 hole spacer it sounds lean. that could cause it to run fat at idle. Make sure the accelerator pump is tight and squirts with any throttle movement. 83 Capri RS T-Top 302, Afr 195 Renegade,11.2 compression, e303 cam, Scorpion 1.82 race series rockers, TFS-R, X3Z w/Tweecer RT, T56 Magnum, 2 1/2" Pypes X pipe w/2 chamber Flowmaster mufflers. Read More, Over the course of just seven months, this ’67 Dodge Dart was transformed from a lively cruiser into a street and strip restomod that shows just as well as it goes. the size and length of the idle well in the metering block act as a idle channel restrictor, we have been slighty enlarging the diameter of the idle well to solve the lean off idle problem we are seeing with a carb like yours. Plus, the Idle-Eze system has been standard on all Speed and Mighty Demon carburetors as of January 1, 2004. Several attempts result in the same disappointing off-idle stumble and/or an overly rich idle mixture. 700 DPs have truck style boosters. Idle Eze throttle plate assm., 850 mech. Try a 31 and go to 72 jets. Out of the box, it was equipped with 74/84 main jets which I changed to 72/82. Read More. The engine should be turned off while you are setting the adjustment on all of the screws. It idles great, has great throttle response, and there is NO STUMBLE now!!!!!! 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. Some my dad use to say, "when you can tell a engine to read so it knows what it's suppose to do, then this stuff will be a lot easier. While I had the carburetor off I checked the accelerator pump squirters and noticed the front was a number 31 and the back was a number 35. https://www.tapatalk.com/groups/racingfuelsystems/index.php, VerticalScope Inc., 111 Peter Street, Suite 901, Toronto, Ontario, M5V 2H1, Canada. 1986-045 Saleen Mustang Griggs GR40, 408W RDI aluminum block, AFR 205, T56. Cars and engines want what they want and that's all there is to it. jet change wont wont fix it. The absolute best carb forum and group of carb guys ever to roam the earth. "For those that will fight for it...FREEDOM ...has a flavor the protected shall never know.". When I first read your symptoms, especially the acceleration stumble that none of the usual culprits fixed, it sounded to me like you have an air leak somewhere. A couple in any direction from stock is normal, sometimes more in the back for racing. Looking inside the carb while you move the throttle does the spray look constant? I can't argue with what works. That's a fair amount of cam for a 355,I like 16 or so degrees initial, think the total is close. it stumbles before you even get into the main jet circuit, and at cruise your still in the idle circuit and you give it gas its going lean, the car finally picks and runs ok when the main jets are just catching up. You drop it in gear, tip in the throttle, and the engine dies. Hmmmm, my 3310-2 has had a 25 squirters since I got it...16 years ago.....it LOVES the 31 in the new 800DP. I would be tempted to bump the initial to 16 and take a couple out of the mechanical along with a bigger squirter. Log in, DAVID VIZARD’S HOW TO SUPER TUNE AND MODIFY HOLLEY CARBURETORS, Drag Racing Traction: Suggestions for a More Consistent and Winning Car, How to Design and Install a Turbocharger System: Step-by-Step Guide, Blueprinting Engines: Valve, Springs, Retainers, Locks, Ford Muscle Cars Handling and Performance Upgrades, Automotive Bodywork: Repairing Collision Damage in a Decklid, Engine Tuning: How to Improve Drivability, Abandoned Dragstrips: Chattanooga Hotspots. Just ordered some 70’s and I’ll report back how it goes. Idle BasicsAll carburetors come with a simple yet efficient idle circuit. There is a theory that I proved wrong many years ago, that says to use smaller jets and a bigger power valve. The first test of a quick fix, after ensuring accelerator pump was functioning properly, was to increase the hot idle speed. I dont think its an acc pump issue, cause it accelerates fine. IMHO and experience,sounds like bumping up the base timing a bit will take care of it. Hook your laptop up and increase your acceleration enrichment by a few miliseconds at a small percentage of TPS change. 10 jet steps say "big problem" somewhere. Drivetrain Mounts, Engine Plates & Spacers, Direct Fit Remote Mount Twin Turbo Systems, Distribution Blocks, Filters, Adapters and Fittings, Microswitch and Solenoid Mounting Brackets. we also relocate the idle jet/restrictor to the lower hole in the metering block. Try 72 jets first, they are the stock set. All the 3310's use 72 front jets, the 70's alone may give you that stumble. Holley carburetors have a power enrichment system that provides fuel to the main power circuit during heavy loads or under full throttle situations. They're numbered according to the vacuum point at which they open. The engine should be turned off while you are setting the adjustment on all of the screws. First off, i know this is quite a common problem with the holley carbs, and and i have searched it at length and tried most of the suggestions that i have come across with no results. How can someone say something is wrong when the car never ran better. With engine warmed up, and cruising along, if I just breath on gas pedal a tiny amount, car hits super lean on wideband and lean surges. The Holley website says 66's come stock on 700 DP's. Trademarks belong to their respective owners. Thanks for the advice. I have a stumble at throttle tip in with my 670 Street Avenger. how big is the cam? For now, Grant has adapted the Idle-Eze idea on new throttle plates available for most of the larger Demon carburetors. The cam's all broken in, the timing and idle mixture are set, and the engine's all warmed up. Idle-Eze throttle plate assm., 650/750-cfm, mech. A forum community dedicated to Chevrolet Chevelle owners and enthusiasts. What squirters in there? If it works, run it. It's pretty easy once you grasp the function of the various circuits. Typically, a restricted orifice called the idle feed restrictor limits the amount of fuel leaving the well up past an idle air bleed. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! Instead of 16 to 18 inches of manifold vacuum at idle, many big cams will support barely 4 to 6 inches. How to ensure your Holley carburetor is using the right power valve for your engine. That is why they are jetted a bit low compared to the others. sound like an adjustment in the acc pump? For a 700, you should have been around 69~71 primary to start anyway. So Grant came up with an elegant solution he calls the Idle-Eze system. 347 Stroker, 10.6:1, Vic Jr, World Jr. heads (2.02/1.60 valves), Custom 780cfm ProSystems 4150 Double Pumper, XE284H cam, MSD E-Curve, 4.30 gears/31 Spline axles, Tremec TKO 5 Speed w/.83 5th gear ratio. it doesnt matter what gear im in, if im just cruising down the road barely on the gas and go to give it a little more, just to increase speed 5mph it stumbles (almost like falls on its face) then picks up. Would a valve not seating properly couse this kind of stuff to happen?? It doesn't stumble If I am hard on the gas. The engine runs great with no flat spots, good off idle transition, WOT ratio around 13:1, cruise ratio of around 14.5:1, and idle ratio also around 14:1. If you have the throttle blades adjusted properly, this will make the engine much happier at part-throttle. Main jets don't usually have much of an effect on off-idle and acceleration stumbles. On the bottom right side of the rear barrels throttle shaft is a small screw that can be used to open the rear slightly so the front can be closed some. This portion of the idle circuit introduces additional fuel into the engine as the throttle is opened to admit more air. I am posting this so that someone might avoid the week of headaches I had trying to get rid of an off idle stumble on my '64 Galaxie. If the primary side throttle blades are set too far open it can cause a flat spot like that. This is interesting. The will make it a little richer on the transition circuit and at idle so you may likely have to go in slightly on the idle mixture screws as well. What you are looking for is an increase or decrease in rpm. Would that be a good place to start? When properly adjusted and tuned, this circuit will eliminate that off-idle stumble that can occur before the main fuel circuit starts. Well if I should have had 71's in it like Kelly suggested, I am only 3 jet sizes over. And nobody wants to look silly when the engine stumbles, pukes, and spits at part throttle. I have a QF 750 double pumper drag race carb installed on my 327. Come join the discussion about performance, production numbers, VIN decoders, modifications, troubleshooting, power adders, DIY tutorials, and more! Idle-Eze throttle plate assm., 850 vac. I have battled those myself and ended up switching carbs. Start the engine and turn one of the idle screws in or out. Off-idle flat spot/bog is one symptom of insufficient fuel to support the amount of air you're letting in with the throttle.


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