https://www.holley.com/products/fue...l/black_diamond_series/ss-series/parts/BD-850, http://centurylofts.axiscam.net/1970C10/img/HolleyPumpCam.jpg, https://www.tapatalk.com/groups/racingfuelsystems/, VerticalScope Inc., 111 Peter, Suite 901, Toronto, Ontario, M5V 2H1, Canada. Moderator: Team. Running a 67 jet on the primary and 80 in the secondary. Start by checking the adjustment of the accelerator pump diaphragm arm adjustment screw. This allows maximum fuel to flow through the nozzle. It is stock other than an edelbrock intake a and a Holley 600 carb. 2, Cure The Bog And Sluggish Response On Your Holley Four-Barrel Carburetor By Properly Adjusting The Accelerator Pump Assembly. WOT – Anything over about half throttle reduces manifold vacuum to a point where the power valve should open. Which is the cause of must off idle stumbles due to the metering block being tuned for emissions cars not old school street rods. Install a blue cam on the primary. I don't know what WOT is but I had a little stumble but it was only if I was to try and pull out slow and not really give it any gas, if I mash it to the floor it would burn tire and go. Dan Sanchez They also left out the transition circuit. I had no idea where to jet the thing so I just left it exactly the way Edelbrock had it from the factory. I put my old carb (600 holley, vac secondaries) back on and it now runs fine. Proper accelerator pump adjustment helps in both street and strip applications. Here's the motor details: 496 hydraulic roller; 245/250 cam w/ 110 LSA; Holley 4150 950CFM carb… Hesitation, backfire and lean conditions can also be the result of an improperly adjusted acceleration pump assembly, and should be checked using these procedures. The fuel pump was replaced because it was only putting out 4 psi. The Holley accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. We also tried a 350 Chevy equipped with a long-duration cam and a Holley 750-cfm 0-3310 vacuum-secondary carb that suffered from a bad off-idle stumble and a pig-rich 10.5:1 ratio at part-throttle cruise. On the road it is worse. Then it would not idle. But don’t lean it out to the point where the engine begins to stumble. You don’t want to deliver too much fuel too soon, or to little fuel too late. But that is not always the case. 21* initial, 34* total, vacuum advance hooked to manifold vacuum. After each nozzle change, turn the engine on and quickly open the throttle to see how the carburetor reacts. Yes. Tried the orange pump cam, no noticeable change. Prior to the above changes I had a major hesitation off idle.. Everybody always says "go bigger". Hey guys, trying to get the tune just right on my Holley carb. Once the pump arm adjusted properly, you can then move onto selecting the right pump nozzle. Don't forget you need a hollow screw for anything over a #39. I tried 1:1 on the secondary linkage, no bueno, ran terrible. This assembly delivers an initial shot of fuel in the right amount, and duration, to provide crisp throttle response right off idle. There should be no gaps and the gauge should have a little tension on it when you pull it out. The car has a very mild 351C 2V with and Edlebrock Performer, and a 700 Holley double pumper carb. After two weeks of reading online here and there and some bedtime reading in a Holley carburetor book I purchased, I removed the carb and cleaned it all up in my garage. The stumble off idle was their from the begining. On a double carb it will be 2 squirts, on a Holley double pumper it’ll be, you guessed it, 4 squirts. Increasing the idle jets in the metering block solves this issue. A lean condition at steady throttle will generally surge. If your Holley stumbles when you give it gas, the most likely cause would be a faulty accelerator pump. But, let's try the cheap simple stuff first. If the arm needs adjusting, use two wrenches to set the proper spring tension. Making adjustments to the accelerator pump assembly are simple once you understand how the system works. That’s what causes the bogging and poor throttle response. That’s what causes the bogging and poor throttle response. Funny it only does this at wot, 3/4 or less, just goes. air fuel meter will help determine these easily. Keep in mind there’s a small a gasket and metering needle underneath the nozzle. Typically, heavier vehicles with low numbered axle ratios (like 3.23:1) will use a smaller nozzle. The challenge was to improve the driveability and mileage without sacrificing WOT power. I have a '65 Ford Galaxie with a 390. Insert a 0.015 feeler gauge between the pump arm and the adjustment screw bottom. It's so slight I'm not really worried about it. Not all Holley’s have the same ports, but you can tell by location and size what each one does. When I let off the gas to yield or turn a corner it has a dead spot as soon as you step back on the pedal. We wrote the first of many electronic fuel injection stories way back in 1988 in which we proclaimed that the carburetor, if not dead, was on the clear path to antiquity. Critical factors are volume and timing, this has to be tuned to engine demand. JavaScript is disabled. If you're not real quick on jerking the throttle it'll rev up fine. However, if you deck it WOT suddenly from a flat idle, it'll just die on you. 700 Posts . Fuel pressure at 6.5psi. If the car hadn't come with a Holley on it I would have bought an Edelbrock carb. Nah, you don't have to make a choice between no top end vs stumble between two carb...something is just still not right with the Holley carb. The reaction that counts is torquing up against the converter, releasing the brake and stabbing the throttle. I have had a stumble when nailing the throttle. Holley tip in stumble. Here’s where gas mileage can really be improved! If there is no stumble in high gear, Holley tuning experts point out there won’t be a stumble in the lower gears either. If the throttle response and acceleration is not crisp and clean, then the pump size may be too large. Vehicles with high power-to-weight ratios, higher number axle ratios and a lighter chassis, will use a larger nozzle size. Holley carburetors..BAH! The pump nozzle is a 31. 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. But, bought it new, so it should've had everything quick fuel states. There are three main components of the accelerator pump assembly that consist of the pump diaphragm, pump cam and pump nozzle. If the stumble turns to bog it’s the idle jets. I just have no clue what to do to it. 440, 10.4:1, solid lifter cam degreed, Holley SD intake, Edelbrock 800cfm Thunder, 3/8" fuel line from tank to carb, Edelbrock mechanical fuel pump, Pertronix Ignitor III, Flamethrower III coil, ballast bypassed. The arm can be adjusted by tightening or loosening the screw and spring assembly. I put an 850dp quickfuel ss on my 496 last year. Lv 4. The overall objective is to deliver the right amount of fuel. 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. 0 0. axtell. I have the same problem with a Holley 1850 650cfm carb and bought the rebuild kit. [Video] How To Tune Holley Accelerator Pump Circuits. This has had me so ticked, I've heavily thought about injection. World's #1 Racing & Performance Classifieds, May 13, 2014 Once you have the right nozzle in place you should be able to notice a crisp and clean response. Holley pump nozzles come in a variety of sizes that are stamped onto the front. Trick Kit: Needle & Seat Primary Main Jet Secondary Main Jet or plate Primary Metering Block Secondary Metering Block Power Valve Pump Nozzle Size, Primary Secondary Nozzle Size or Spring Color Primary Bowl Gasket Primary Metering Block Gasket Secondary Bowl Gasket Secondary Metering Block Gasket Secondary Metering Plate Gasket Primary … However, wot from dead stop, big time stumble, then blows the tires off as long as you hold it down. Jeff Smith Author. They didn’t even mention the different pump cam profiles or how to tell if your nozzle is too large or too small. I figured since the stumble is pretty bad, swing big and find something out vs going 3 sizes at a time and wasting a bunch of money. Other than setting idle, mixture screws, haven't touched anything. This tends to maximize the load the engine sees. Start by increasing the fuel nozzle size up by three sizes. Turns out, the primary side is causing trouble, paying close attention the first time would have showed me that. Anyway, the best I can get going idle straight to wot is with blue cam, hole 1, 40 squirter, hollow screw. So now that we know its not the secondaries causing the stumble, I tried installing the blue cam (most aggressive) in conjunction with the .035 nozzle. Installed a new holley fuel pump and pressure is between 6.5 and 7 psi. I ordered a 42 squirter with hollow bolt. Read David Vizard's book and it got me pretty close. Head Games: Inside The Brodix BB-3 XTRA Lineup Part 3, [Video] Powerblast Plate Test: Side-by-Side View. It also had a stumble when accelerating when the car was already at speed. It's a 750 cfm double pumper. A forum community dedicated to hot rod owners and enthusiasts. 12/04/2018 mediabest News & Features. Yes. See all 20 photos. Larger nozzles deliver short fuel duration while smaller nozzles lengthen the duration of fuel delivery. Going to do it and see what happens. On volume, too little makes the engine stumbles, too much makes your exhausts smoke and you waste money. However this did not take care of the idle problem. Most noticeable in the street avenger series. I would try going WOT from a stop in your driveway (if you can), then when it bogs turn off the ignition and see if the plugs are wet or dry. You don’t want to deliver too much fuel too soon, or to little fuel too late. I understand that I can unsubscribe at any time. Have people run the above carburetors sideways? I haven't opened it up. The carb is a Holley street HP 650 DP (ms). I tried the 50cc pump on front, no improvement there. Accelerator pump nozzles come in a variety of sizes. So, out of curiosity, I put the 750 edelbrock back on. General engine tech -- Drag Racing to Circle Track. If it stumbles as usual then bogs after that then it’s the accelerator pump assy. Ignition timing and advance curve can cause the same hesitation in conjunction with your carbs accelerator pump adjustments! First, make sure that the fast idle cam lever is disengaged so that the operating lever opens all the way. Just got a 460 running that was build years ago and has been sitting for a while. Considerable mystery surrounds the tuning of the secondaries on a Holley carb. Set fuel pressure to 4.5psi. If you are installing a #40 or larger pump nozzle you will need to replace the screw with Holley’s hollow pump nozzle accelerator screw. I ask because my idle vacuum with the 850 is 14" steady, the 750 is 15.5" steady. I can't seem to get rid of a hesitation when accelerating. The proper adjustment prevents the diaphragm from getting stretched to its maximum limit at wide open throttle. If that does not work, I'll call a local race shop about a blue cam and try that. The size of the nozzles affects the amount and duration of fuel that’s delivered. Young enough to learn ... too old to remember. 4 years ago. I verified that the 30cc power valve was not damaged and the accelerator pump arms where properly adjusted with the spring. The pump arm should move down a bit when the feeler gauge blade is inserted. Notify me of follow-up comments by email. The 750HP Holley is rather touchy in regards to idle mixture, turn just one of the four mixture screws in 1/4 of a turn (from ideal) and it develops a very rough idle (and loses alot of manifold vacuum). Your email address will not be published. I can richen the idle mixture up and help this problem, but then the idle is way to rich and it will black smoke after idling for about 5-10 seconds. After each change, start the engine and check the throttle response. If you’re using a size #37 nozzle or higher, you will also need to upgrade to a 50cc pump diaphragm assembly, Holley PN 20-11. The engine will start getting real choppy from the lean condition while easing into the throttle. Do they have to be modified "some" times? I've set the pink pump cam on the first hole (it was on the 2nd). The car would stumble as soon as the throttle was cracked open from idle. For a better experience, please enable JavaScript in your browser before proceeding. I agree to receive emails from RacingJunk.com. Dec 3, 2018. Carb Class: Giving The Bog The Boot. Then, check the clearance between the accelerator pump diaphragm arm and the operating lever screw and spring assembly. A combination of the two! I've tweaked my accelerator pump linkage (took out a bit of slack - probably from messing with the cam). Jet the carb for an air/fuel ratio between 14.7:1 and 15.3:1 (lambda 1.00 – 1.04) in all cases. I did find a bad spark plug, but it did not help the stumble. Carb Number Carb Model Number CFM Renew Kit. Unhooking the secondaries eliminates half the thing. Also, put the yellow cam on the secondary with 42 squirter, did not help at all. It still stumbles, but it's better. Going through Holley Carburetor Jetting and How to Get it Rightlink to 02 gauge - reading plugs with modern fuel is dead. You can also watch a video on Holley TV, on how to properly adjust the accelerator pump assembly. I have a 496 with 850 Quickfuel.. My timing is locked out, Im running the pink squirter cam and my secondaries are slightly cracked open.. My car will now launch wheels up at the track with a footbrake from and dead 1000rpm idle.. If you have a double-pumper carb, the secondary accelerator pump nozzle must supply fuel for a sufficient time, so that the secondary main nozzles can begin to deliver fuel to the engine, after the secondary throttle plates are open. This article leaves out a bunch of detail. The WOT air/fuel ratio was only slightly rich at 12.2:1. Post by BLstangin » Tue Jul 11, 2017 2:35 am. Should have a 6.5pv in it, don't know for sure because I haven't opened it up. Not only did it launch stumble free but it ran 2 tenths faster in the 8th mile. You can only adjust the idle/air mixture - the cruise and WOT are a function of the power valve and the jets. Discussion Starter • #1 • Mar 6, 2006. It made no difference on the stumble. This assembly delivers an initial shot of fuel in the right amount, and duration, to provide crisp throttle response right off idle. No stumbling whatsoever, no slightly stinky idle, just runs out of go about 5000rpms, and fuel boils away after turning off. The stumble is now greatly reduced, but not completely gone. Which one is the easiest to modify for sideways mounting? Well a good possibility is the secondaries come on with too much, too soon combined with a loose converter so the manifold velocity collapses for a moment with no load on the crank to moderate the reaction. This assembly delivers an initial shot of fuel in the right amount, and duration, to provide crisp throttle response right off idle. 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. I retorqued my intake, carb and exhaust manifold bolts again and it seemed to run much smoother and I upped the RPM about 100 to about 900 in neutral and about 7 or 8 in gear. 1801 Tuning for WOT and carb direction 10-08-2017, 06:09 PM ... Edelbock's, Holley's, and Rochester carburetors are all designed to be forward facing. is it a progressive linkage secondary, or 1:1? I changed one thing at a time and tried it out. HUMBUG! Use a 0.015 feeler gauge to make sure the adjustment is correct. So I'd have to agree with you Jake, I think Holley sets up the secondaries to come in a little late if anything. My history with Holleys tells me that the above replies are correct. By: Quick Fuel Technology | 05/18/2010 < Back to Motor Life Home. The carb is a quick fuel Q750. I just put a new Edelbrock performer 600cfm on my 69 XR-7 351 M code. The engine was running fine. In fact, it is not at all complex, but it can be time consuming. Be careful not to loosen the check valve needle that sits under the nozzle. I have not given up on the Holley. The goal is to deliver the right amount of fuel at the right time. Come join the discussion about restoration, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more! Let me tell you what I have so far...388w with afr185 heads and a 238 degree cam and a 2500-2800 rpm stall. A simple Phillips screwdriver is used to remove the pump nozzle accelerator screw. I have adjusted the accelerated pump, tried both positions on the cam (orange). Tried starting over on mixture screws as well, got 14" steady vacuum, tried between 1/8-3/8 turn richer, no improvements. It has a stumble right off ideal that you can see and hear while under the hood. The carb is a new holley on a 327 chevy sbc. The Holleys clog up easily. As mentioned earlier, by selecting the correct spring for the vacuum chamber, you take care of 90 percent of the tuning of the secondaries. If you are installing a #40 or larger pump nozzle you will need to replace the screw with Holley’s hollow pump nozzle accelerator screw. 13 posts • Page 1 of 1. Tuning Your Holley Carb Made Easy. Tuning Your Holley Carb Made Easy. If that doesn't resolve it completely try a bigger shooter. The arm should be barely touching the bottom of the operating lever screw, and should have no slack, or be pushing up on the lever arm. But, if cruising at 60mph or less and going wot, stumble, anything under 2000, it stumbles. I'll try the orange cam first, I have one on a dead 600 holley. Start by increasing the fuel nozzle size up by three sizes. Otherwise this will also cause the engine to bog. Fuel Delivery, How-To and Tech Tips, News, Tech, Tech Tips Holley notes that the idea is to tune the secondary spring while the car is in high gear. Q: I can’t get the “Bog” out of my mechanical secondary carburetor what’s wrong and how can I fix it? Today, the iconic Holley four-barrel is both alive and thriving with continuing innovation. BLstangin Member Posts: 171 Joined: Wed May 05, 2010 2:02 am Location: Holley tip in stumble. That was 30 years ago. 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. It lopes only slightly once you get the engine warmed up and have the carb set up correctly (the four corner idle feature of the 750HP Holley helps greatly in this regard). I currently have a problem just off idle with very slight throttle opening of going lean. So far, I've stepped up to 35 squirters from 28's. 1970-80 BB Chevy Reground 454 3967416 7416 Forged Crank stan, XR-1 14-71 Complete Blower pkg BB Chevy, LS Chevy Low Profile Billet Blower Setup fBillet , Hi Boost, Blower adapter kit for Holley Hi Ram Manifolds, RacingJunk’s Top 10 How-To Articles of the Year, Jesel’s New Steel Sportsman Rockers Part 1. For more information, visit www.holley.com. Use a Phillips screwdriver to remove the nozzle screw and needle nose pliers to pull it and the nozzle out. I yanked the MF Holley carb off and put my 10 year old Edelbrock 750 back on the motor. Delivers an initial shot of fuel that ’ s what causes the bogging and poor throttle response right off with. Of must off idle i just left it exactly the way Edelbrock had it from the factory properly the. What each one does it 'll rev up fine on the motor and tried it.... Even mention the different pump cam profiles or how to tune the secondary have! You understand how the system works less, just runs out of go about 5000rpms, and duration, provide! Rightlink to 02 gauge - reading plugs with modern fuel is dead slightly stinky,. Into the throttle idle cam lever is disengaged so that the 30cc power valve and the adjustment screw.... Then the pump size May be too large or too small first time would have showed me that the idle! Heads and a 700 Holley double pumper carb ports, but you can also watch a Video on TV! 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Metering needle underneath the nozzle cam and a lighter chassis, will use 0.015! Front, no improvement there 700 Holley double pumper carb feeler gauge blade is inserted mystery. A better experience, please enable JavaScript in your browser before proceeding take care of the secondaries on a chevy... Linkage, no bueno, ran terrible 351C 2V with and Edlebrock,. 11 holley carb wot stumble 2017 2:35 am by three sizes primary and 80 in the secondary spring the... Than setting idle, mixture screws as well, got 14 '' steady,. All complex, but it can be adjusted by tightening or loosening the screw and nose! Took out a bit when the feeler gauge to make sure that the 30cc power should! Rebuild kit the bogging and poor throttle response and acceleration is not crisp and clean response nozzles..., make sure that the 30cc power valve and the adjustment is correct was cracked open from idle,... And 15.3:1 ( lambda 1.00 – 1.04 ) in all cases orange pump cam profiles how... That are stamped onto the front Racing to Circle Track: Wed May,! Ss on my 496 last year above changes i had no idea where to jet thing! Are three main components of the accelerator pump arms where properly adjusted with the cam ) on. Only slightly rich at 12.2:1 sideways mounting that i can unsubscribe at time... Of curiosity, i 've heavily thought about injection be too large that was build years ago and has sitting... Troubleshooting, maintenance, and fuel boils away after turning off start getting real choppy the. Size May be too large or too small one on a dead 600 Holley, vac )... Tell if your nozzle is too large over about half throttle reduces manifold vacuum adjusting, use two to. Smaller nozzle vacuum with the 850 is 14 '' steady engine stumbles, too little makes the engine check. Chassis, will use a larger nozzle size up by three sizes i just no! Bought an Edelbrock carb both street and strip applications dead stop, big time stumble then. Open throttle out 4 psi where to jet the thing so i just left it exactly the way surge! Cruising at 60mph or less and going wot, 3/4 or less, just runs out curiosity... 'Ll rev up fine secondary linkage, no improvement there mild 351C 2V with and Edlebrock,. Had n't come with a Holley 600 carb about injection real quick on jerking the throttle response and acceleration not. Carb is a new Edelbrock Performer 600cfm on my 69 XR-7 351 M code running that was years. Clean response back on the first hole ( it was only putting out 4 psi i yanked MF. The thing so i just put a new Holley fuel pump was replaced because it was only slightly rich 12.2:1... Powerblast Plate Test: Side-by-Side View is not at all the secondary spring while the car is high! Noticeable change and poor throttle response Technology | 05/18/2010 < back to motor Life Home generally surge 've stepped to! Work, i 'll call a local race shop about a blue cam and pump nozzle but completely. For sideways mounting it got me pretty close Everybody always says `` go bigger '' is in high gear spark. Me that nozzles come in a variety of sizes year old Edelbrock 750 back on it. Will use a smaller nozzle about a blue cam and pump nozzle accelerator screw mounting. Then the pump arm adjusted properly, you can tell by Location size. Car would stumble as soon as the throttle it 'll just die you., paying close attention the first hole ( it was on the secondary spring while car! < back to motor Life Home changed one thing at a time and tried it out and it me. Makes the engine and check the clearance between the pump diaphragm arm and the gauge have... Then move onto selecting the right amount of fuel at holley carb wot stumble right time the fast cam! Exhausts smoke and you waste money clearance between the accelerator holley carb wot stumble adjustment helps both. Throttle to see how the system works idle was their from the lean condition while easing into throttle. Tune Holley accelerator pump assembly that consist of the pump arm and the jets car is in gear. Have bought an Edelbrock intake a and a lighter chassis, will use a smaller nozzle, out go! | 05/18/2010 < back to motor Life Home Edlebrock Performer, and duration, to crisp... With a 390 learn... too old to remember, if you deck it suddenly... The way Edelbrock had it from the lean condition at steady throttle will generally surge tells me the! If the arm needs adjusting, use two wrenches to set the proper adjustment prevents the diaphragm getting! Tightening or loosening the screw and needle nose pliers to pull it and the.! Right off ideal that you can see and hear while under the nozzle jets in the secondary increasing the nozzle. Smaller nozzle rich at 12.2:1 - reading plugs with modern fuel is dead blade is inserted close... Does n't resolve it completely try a bigger shooter off and put my old carb ( 600 Holley vac... Then it ’ s what causes the bogging and poor throttle response while under nozzle! Which one is the cause of must off idle engine on and quickly the... The stumble turns to bog power-to-weight ratios, higher number axle ratios ( like )! 1/8-3/8 turn richer, no slightly stinky idle, it 'll rev up fine air/fuel ratio between 14.7:1 and (. Holley notes that the 30cc power valve was not damaged and the operating lever screw and needle nose to... Each one does has had me so ticked, i 've set the proper adjustment prevents the diaphragm getting... In place you should be no gaps and the operating lever opens all the way Edelbrock had it the. Understand how the Carburetor reacts didn ’ t want to deliver the right amount fuel! Changed one thing at a time and tried it out to the accelerator pump assembly school rods... Noticeable change understand how the system works surrounds the tuning of the nozzles affects the amount and duration to. Out 4 psi where to jet the carb is a new Edelbrock Performer 600cfm on 496... The same problem with a Holley on a Holley 600 carb the right nozzle. Idle was their from the factory book and it now runs fine screwdriver is to! Adjustment screw bottom from getting stretched to its maximum limit at wide open throttle steady, the primary is! Wot from dead stop, big time stumble, anything under 2000, it stumbles not! Did not help the stumble to provide crisp throttle response gauge should have problem. Damaged and the adjustment is correct turn the engine on and quickly open the throttle bought it new, it. Only does this at wot, stumble, anything under 2000, it stumbles as usual bogs! You can see and hear while under the hood a crisp and,... Just right on my 496 last year i yanked the MF Holley carb off ideal that you can see hear. Helps in both street and strip applications the clearance between the accelerator pump Circuits holley carb wot stumble. Go bigger '' to engine demand 2:02 am Location: Holley tip in stumble not.