If there is a bog or hesitation when the secondaries open, the spring tension is too light, go to the next heavier spring. The Holley secondary springs regulate the opening point and rate on a vacuum secondary Holley based on venturi air velocity. 059 main feed and. These options make it right for a wide variety of applications. 44 Plug gap. Very easy to install. If I ease into the accelerator it dosent bog to bad but show more I have a sbc with a holley 650 and I'm not getting the power I should. And even the old Rochester 4GC carb is a mechanical secondary carb that uses an air valve. you only have the primary p/v and jets to work with. 76 secondary), along with T-10 4spd and 3:90 gears in corporation posi. a mech secondary 4-barrel would behave like a 2-barrel if the driver mooshed the go pedal). The carburetor that we would recommend is based on how the customer will drive their car and the engine package that is in the car. Enough people were compaining about a bog that I thought I'd see if it could be fixed. I bought a used draw through turbo setup (T3,. The springs are color coded and the instructions tell which to use to delay or increase the opening. 202 carby set-up WW Stromberg or 350 Holley or ? - posted in Engine: G'day All I am going to fit extractors to my wife's LX Hatch and as I've had a bit of trouble with the single choke Stromberg on it, I want to change to a double choke carby. I have a similar 400. Holley Vacuum Secondary Springs published by Holden Fan (not verified) on Wed, 25/01/2006 - 14:08 I have been trying to fine tune my 465 holley to get rid of the "bog" when I floor it. Your secondarys probably don't start to open until 3000 RPM. 076 main feed and. I take it you are talking about a Holley carb. Lacking a digital camera, make a drawing as accurate as possible that will show where things go. Mine has a Powerglide 3. I have a 750 Holley vacuum secondary on it right now. Check the primary jets first. It has a Edelbrock Performer intake and a 4160 doub. Increasing accelerator discharge helps but I believe is a band aid. lunati 61605 hyd flat tappet. I have used a 750cfm Holley on a stock 351W and after jet changes and idles adjustments, the thing ran great. Stumble should now be reduced, perhaps significantly. Off Idle Bog Hi, I recently got a car with a Holley carburetor on it, and first of all I can't find it listed anywhere. If he was I can't imagine there'd be any bog because the secondaries never close at all. a Holley 3310 (sometimes called a 780 vac sec) then its actually the factory carburetor for a 440 1970 and earlier. 35" power valves in both blocks, 72 primary main jets, 73 secondary. Holley 750 CFM 4 Barrell Carburetor 3310-3. The real advantage to these carburetors is that they can be. 27 1st gear, 1. The specs are: 10:1 compression ratio Edelbrock Performer RPM Aluminum Cylinder Heads Edelbrock RPM air-gap intake Summit Full Roller Rockers (1. Stuff a rag, or towel down the carburetor throat to prevent you from dropping anything down the carburetor. You could also look online about vacuum secondary tuning, or buy/borrow a Holley book. See our Performance Carburetors, Intake Manifolds, Cylinder Heads, Crate Engines, Electronic Fuel Injection. Does your vehicle have a bog or stumble when you try to accelerate?. I have had the car 16 years and from time to time I have tried to solve the problem. its a street car. This is a good looking carburetor. Now, Holley EFI products power these cars and are dominating the performance world. 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. You can start heavy, with black or brown, and keep moving up until you get a bog when you go WOT, then go back one spring. Threw that on there and runs great. 5 tons around and will bog if you put the gas to it to fast. My favorite pre-school toys were a Packard carburetor and a set of tools. A "properly" sized 4bbl will have the vacuum secondaries completely open at full load at maximum RPM. The #1 cause of the dreaded "bog" is the too light "medium" stifness secondary spring 390 comes with, you'll probably need to switch to a Brown [medium high] spring which will delay the opening of the secondaries by several hundred RPM. Under cruise conditions, the fuel-air mixture is determined by the primary main jets (there are 2 of these for the front two primary throats). The amount of vacuum does depend on a lot of factors, but just to clarify there is vacuum even at WOT. my carbshop holley 750 blow thru carb has overly rich idle. You have the correct carb for your car and it came that way from the factory. When the carb is assembled and adjustments made to spec, turn your attention to the secondary air valve rate of opening. HOLLEY (2 Screws) – 1 to 2 TURNS FROM SEATED. Although they do have the air door to regulate air flow, they are 100% mechanical in nature. I KNOW this is too big. You would need to ask Holley how to determine that. Lacking a digital camera, make a drawing as accurate as possible that will show where things go. hitting a max. it's too big. As rpm increase, so does velocity through the primary venturi,. A few years ago I ran a 700 CFM race carburetor with vacuum secondaries and it seemed to run better. The free heights and installed hieght in a Holley Quick Change vacuum pod were measured with a vernier caliper. the engine it is on pulls about 10 in. Choke is working proper, set accelerator pump to specs and it seemed worse. Although they do have the air door to regulate air flow, they are 100% mechanical in nature. Properly set up, considering your manual transmission, the Holley 600 would have outperformed the Edelbock 500. Thought it might be helpful to post what I've collected on vacuum secondary diaphragm opening rates. carburated 302 holley 750 bogs down from 3800 - 4300 i got a carburated 302 with the 750 holley carb manual chike vacuum secondarys and it seems to bog down when i get around 3800 to about 4300 once i get past that its fine are there and carb guys out there that can help me. ” On a Q-Jet, we see that we can control the fuel mixture throughout the operating range. In example two, a HOLLEY® 4779 750CFM mechanical secondary. While the Holley ran well (and got 19MPG on the bash trip) it just did not have the punch that the old MSD EFI system had. The carb is a Holley and I was able to narrow the cfm down by the # stamped on it which is 8879. Probably the most important factor in getting 3×2 carbs to work right is vacuum and the strength of the springs in the vacuum secondaries. I believe it is a 750 but I am not too familiar with carbs. A dualstage carb has a primary side that supplies the air/fuel mixture throughout the entire stage of engine operation, and a secondary side that operates only when the engine demands a greater quantity of air and fuel. The 950 was available however from holley. Some applications may require the use of a Holley to Ford/Ford to Holley tapered port adapter to get the correct barrel spacing to mate to your existing manifold. 0 inch Primary throttle bore diameter is listed as 1 5/16 inch Secondary throttle bore diameter is listed as 1 5/16 inch Hope this helps!. 5 Power Valve with Power Valve Fuel Passages of. choke horn removed. another thing to consider is vehicle weight. 6) Lunati Voodoo Cam- 219/227 at. A vacuum secondary carb will be more forgiving if your clumsy on the gas pedal, it will run smoothly and give you good throttle response over a wide range of conditions. What will cause this?. We currently have a 383 with a Braswell 850 with mechanical secondary, ( we have also ran the same carb on our 410 & 415 small blocks) some times a out of the box carb just doesnt do it, get with a carb specialist like braswell, its money well spent. I guess it was tuned right, or one of those Wednesday cars or something, because for that car, the 780 was perfect. Sometimes you can an idea of when the bog occurs to help determine the cause. My Carburetor is Leaking at the Throttle Shaft. I have not used a vacuum secondary carburetor on a 300 six because it responds well to mechanical secondaries without a hint of bog. Definitely not too much, as the carburetor will only deliver the CFM the engine demands. Sean Murphy showed us how to do it. If you're determined to use that 750 Holley, you can still get it to run very nicely with some. Rated 5 out of 5 by Mr Fixxit from Increased performance I was informed that this kit would eliminate the off idle bog that I was having with my Holley carb. Of the three, the most accurate is the vacuum guage method, best to have one for each carb, but it's not absolutely necessary. New 3-14-01 This tech paper will discuss basic set-up and tuning of Holley vacuum secondary carbs for optimum street performance and drivability. Finished up putting the intake and carb on my '82 today. Carter did. Think of it this way, accel pumps are battle axe ways to give fuel, jets are precise, PV restrictors are also precise. 7 310 HP, What is the best carb to run on the set up. A mechanical secondary carb may be able to cause a nearly zero vacuum when you first crack the throttle open at lower. Holley Carburetors. On this mild cammed engine, the carburetor would utilize a standard 2 corner idle circuit system, a power valve with a vacuum rating between 6-9 inches, and a relatively standard tuning set-up. Although often disregarded as a true "performance" carburetor, the vacuum secondary Holley is one of the most flexible and easily tunable units around. this could be the cure! engines with high compression / large duration camshafts require more fuel during acceleration. After running the 670 Holley on the 427 in my 66, I decided I would try a little bigger carb. Use a vacuum pump hooked up to the fuel inlet via a 3/8 metal line. Next, consider the applica-tion, or how the vehicle will be operated. 035 Squirters, a 6. Often with mechanical secondaries, the transition is very noticable as a 'thrust' of power. Holley carb tuning takes time to dial in. That may be the best solution, I assume the pickup bleed in the secondary venturi is open. The #1 cause of the dreaded "bog" is the too light "medium" stifness secondary spring 390 comes with, you'll probably need to switch to a Brown [medium high] spring which will delay the opening of the secondaries by several hundred RPM. 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. I used to get 300+ HP from a 351C with a torque cam and 600 cfm Holley vacuum secondary carb, yet get 19-20 mpg in the highways. As airflow increases through the primary throttle bores, the secondary diaphragm senses that and begins to open. Once you back off the throttle a bit to shift the secondary pulloff has full vacuum for a second and then the secondary air plate slams shut and it has to go through the whole process of opening up again and has to get the air and fuel moving. On the Ford dual quad setups there is that hose that ties both diaphrams together to supposedly let both sets of secondaries open together at same rate for balanced fuel distribution. Instant response, no bog and great performance. He was right. The secondaries were not opening with the standard spring that the 3310 comes with. this would mean that I need to change the power valves from the 6. The Holley secondary springs regulate the opening point and rate on a vacuum secondary Holley based on venturi air velocity. Vacuum gauge connected to intake manifold port just aft (stbd side) of carb. If I step on the gas (moving) it will bog down and will die if I hold the accelerator down. Holley 83670 670cfm Vacuum secondary carb with the stock 65/68 jets and 6. made improvements but it was always there. If you want a good combo for a mostly stock 305 Chevy, a 600 cfm Holley vacuum secondary carb and an Edelbrock Performer intake manifold would be a good choice. The big four suppliers of 4 barrel carburetors today are Edelbrock, Holley, Quick Fuel and Barry Grant, each of these carburetor designs have strong and weak spots. The double pumper ( mech. Being a 4160, it doesn't allow for changing jets on the secondary side so I purchased a conversion kit and pulled the carb off. Mechanical secondary, hit it too soon and you could hear the bog for miles! The only thing it worked on was a Racer Brown cammed 440 magnum. The secondary was vacuum operated, and had a larger vacuum pod than the 4bbls did. "For most street cars and even many street/'strip applications, a vacuum-secondary carburetor works best," says McFarland. For instance, if the vacuum gauge reads 9 inches, a 4. keep track of your steps. When I installed a 750 dp on my almost stock 360 drag motor it had a bog, the 650 did not. if i come up on the convertor a bit it doesn't bog when i go wide open. 0L HO Mustangs Came With A Holley Four-Barrel That's Different Than The Typical Holley Performance Carburetor. I would like to hear from those that are using Vacuum Secondary and Mechanical Secondary carburetors. Personally I always use mechanical secondary carbs as they are far more responsive , but not perfect , if you floor a mech carb at too low RPM or with too much load I promise it will bog the engine simply cannot overcome the vacuum drop , but if you punch it half way & roll in it will out perform a vacuum carb everytime , , at higher RPM mech. Carter AFB carburetors are nearly identical, that is why I com bined the two into a single guide. But while going 45 or better it hauls ass and has good power. The pump serves to inject an added boost of fuel to eliminate bog or lag when the throttles are opened, which is especially critical at lower engine speeds. Keep in mind the idle screws and chock really do very little to correct anything except idle and cold starts (something many people don't understand). Before the purchase, I made a couple of calls to satisfy my curiosity about this carb which, as many have pointed out, looks strangely like a Holley 4010. I have never had good luck with vacuum secondary carbs on a race car or pre runner. I know holley advertises it as a gas mileage gig, which I think is kinda stupid. with the secondary springs, keep changing for lighter springs until you feel a bog and then use one step heavier. I have an engine similar to yours for cam size wise and I am running a holley 650 vacuum secondary at the moment and jetting that is good for them is about 66 primary and around 74 secondary as a starting point and a 750 needs bigger jetting cause they have bigger throttle bores which allow more air in thus they have to have bigger jets in the. It runs great, the only thing is that taking off full throttle it still feels as if its bogging some. A 600 cfm with vacuum secondaries on a stock 289 will open the secondaries very late (full throttle, high rpm). They have great Installation Instructions for Holley 0-83570. I also agree that a vacuum secondary would be a far better choice for a huge car like this Grand Marquis, especially if this 460 is a low compression unit with stock gears, and a stock cam. summitracing. If the air valve opens too quickly, the engine will bog. If I put on the power smoothly, its fine. Problems like these are a non-functioning accelerator pump in about 9 out of 10 cases in my experience. So, I was thinking that the vacuum secondaries are opening too soon and it likely needs a spring kit to tune it? The pump shot seems strong and the bog is too long to be related to that (IMO). When i step on it and the secondaries open up i get like a space or a flat spot when those open it up. Vacuum secondaries are designed to open when the engine is under load. What will cause this?. 6] the secondaries on a Holley Vac secondary carb are adjusted with springs which are changed to a lighter spring until a bog is felt from the secondaries opening too soon you then install the next stiffest spring, & springs are available in a kit Or you can get the double pumper Holley & manully control the secondary with the throttle position. And it stayed on since around 2004. Ive found the 650 with vacuum secondary venturis the best all round, I'm not the mechanical whizz but it can be tuned so I can putt around to save fuel, or open up and light them up. Hey folks, need a pro's suggestions, so I came here. of 5,500-6,000rpm. Avenger Tuning Issues Bog/Hesitation/Miss If this is your first visit, be sure to check out the FAQ by clicking the link above. M110 carby replacement and Holley At a certain vacuum level the secondaries will open, referenced to vacuum (and the tension in a spring in the vacuum diaphragm. The video describes the various rate secondary springs, how to change them, and the testing procedures to follow to make sure the secondaries open properly for best performance. The ZZ4 is rated at 355hp and I thought the Street Avenger was a great carb on it. Holley vac secondary bad stumble on non-cruise accel? Holley Street Avenger 670 Bog. 63 hesitation/bog from take off - Buick Riviera - Riviera Quadrajet Info by Lars - Corvette Forum : DigitalCorvettes Demon wants to tell you how to tune carburetors—in minutes. 08 but launches like a big coil spring with that Holley 390, no bog at all. Holley had a major bog right after idle. What I do know is the car runs very rich. I don't know your altitude. If you have a secondary plate. It can be susceptible to bogging if either the accelerator pump linkage has too much play or if too light a spring is installed in the secondary diaphragm housing (in the case of vacuum secondary carbs). In 1983-'85, The 5. but i cant get rid of this off idle bog. What carb were you running before you put the Holley on? My Little Y Block Page. Holley site says. If the dashpot is malfunctioning and if the spring is too loose, for example, the door will open too soon (before vacuum has a chance to build during acceleration) and a bog will occur. The primary wells seldom leak, the secondary wells on the early (1968-back) carbs do leak much more often than the later carbs. It could be that some people don't know it was there to start with. Likewise a carburetor with vacuum secondaries will only open the secondaries enough to feed the engine what it needs. Edelbrock Performer RPM intake manifold. Here's what my intentions are: 7. Remember, the vacuum secondaries are controlled by vacuum, not RPM or throttle position. When the vacuum gets high enough, it overcomes the tension of the spring and moves the diaphragm. Holley Street Avenger Instructions Holley's Street Avenger line of carburetors has a reputation for bolt-on-and-go performance. Had Holley 750 vacuum secondaries on shelf in garage. 5" before it opens, and that 'wait' is a lean spot. With a double pumper,they open every time the throttle's opened all the way,but you have squirters on all 4 barrels,so no flat spot/bog. A vacuum secondary carb will be more forgiving if your clumsy on the gas pedal, it will run smoothly and give you good throttle response over a wide range of conditions. Now, Holley EFI products power these cars and are dominating the performance world. When the vacuum secondaries are operating properly, the transition when opening will be smooth without any noticeable bog or jerking in the acceleration. Only the Holleys and the old Autolite carb that use the vacuum pod to open the secondary throttle plates are considered as vacuum opperated secondary carbs. So with that am I flushing gas on the street, because my old Holley vacuum secondary spreadbore is a 1 to 1, however the back only opens when the diaphragm and spring are overcome by the signal. Mechanical secondary, hit it too soon and you could hear the bog for miles! The only thing it worked on was a Racer Brown cammed 440 magnum. If the nozzles do not start by the time the pump shot expires, bogging will result. Alright guys, im tired of fooling with my edelbrock 1407(750cfm) I know i can get her tuned better with the Holley, but what should i go with? Im looking at the 750 or 800 double pumper, or the 750 vacuum secondary carb, maybe even the 770 street avenger?. Other carbs have notches milled into the throttle blades right at the transfer slot. It's much easier to tune a vacuum secondary for the street. this way you can nrrow down if its a primary or secondary issue. An important point should be kept in mind when tuning a double pumper: The secondary accelerator pump must supply fuel for a sufficient time so that the secondary main nozzles can begin to flow fuel to the engine after the secondary throttles are opened. 8" of vacuum is enough for brakes. Are you sure the bog is from too much fuel? Could be lack of fuel, try going to a very light secondary spring and see if it does the same thing. Of course I'm running a vacuum can to operate the power brakes and headlights. On carbs with vacuum secondaries, the accelerator pump system is typically installed on the primary side only. Ported and manifold vacuum will deliver the same amount of vacuum advance any time the throttle is open. Wow, and I had to tune out an off idle stumble when I went from Holley to Edelbrock (of course my old Holley was a vacuum secondary so maybe that's why it was so smooth). Floats: Most floats on Holleys are externally adjustable, except the Quadrajet replacement carbs, series 4175. Very easy to install. Some say I should run a vacuum secondary carb. A kit with a number of different calibrated springs is available from The Carburetor Shop LLC. Holley Carburetor Full Power Circuit Calibration Guide July 27, 2015 by Muscle Car DiY Strange as it may seem, the main jet on a Holley carb is not what you should be using to calibrate the WOT mixture delivered to the engine. Yes, the Holley secondary diaphragm is controlled by the vacuum signal at a small port in one of the primary venturis. 5 would have to wait for the vacuum to drop to 3. It makes it almost impossible to do a nice burnout, cause i can nail the gas right away. I would take the mechanical linkage off of the outboard carbs and get two holley vacuum secondary spring kits and install the small yellow spring in the outboard carbs so they open sooner under vacuum Get them back to stock configuration, but put the a lighter spring in the outboard vacuum pods. General Tech - symptoms of wrong power valves in holleys - I 've got a 650 with mech. The only carbs that I can think of that are considered vacuum operated secondary four barrel's are the Holley's and the old Autolite carb used in the 60's that also used a vacuum pod to open the secondaries. I have a sbc with a holley 650 and I'm not getting the power I should. The problem Im having is when I really stand on the throttle there is not much bottom end, its okay but could be better (could be timing) but, when the engine develops RPM, the car kind of surges a little and then goes again. We currently have a 383 with a Braswell 850 with mechanical secondary, ( we have also ran the same carb on our 410 & 415 small blocks) some times a out of the box carb just doesnt do it, get with a carb specialist like braswell, its money well spent. But I wanted to compare it to the edelbrock. So as a temporary fix I zip tied the linkage to bypass the vacuum. It has #72 jets in it. I had to use a pretty light spring in my old Holley 600 to get it to run right. If you make 7"-8" of vacuum at idle you should be able to get away with a 6. These options make it right for a wide variety of applications. Often with mechanical secondaries, the transition is very noticable as a 'thrust' of power. The change could not have amounted to more than a quarter of an inch. 050'" transition slot uncovered, 1/16" holes in primary blades. Put a BB in the hose. If you have a vacuum advance distributor and it is hooked to direct, manifold vacuum, NO amount of playing with the carb will get rid of the bog, Find a 'ported' source or just disconnect it and plug the hose entering ignition and re-set the initial timing. The Holley websit can help you choose what application you need for best performance all around. Find helpful customer reviews and review ratings for Holley 0-90670 Model 4150 Truck Avenger 670 CFM Square Bore 4-Barrel Vacuum Secondary Electric Choke Carburetor at Amazon. The springs are color coded and the instructions tell which to use to delay or increase the opening. With the 450 in question,you get all 4 barrels opening at once when you mash it,like a double pump,but w/o squirters for the secondaries,so you get a tremendous lean. Now if that is the case why did Chrysler choose to not use this on their 426 Race Hemi cross ram setup using vacuum secondary 770 Holley carbs. The secondary rods are a high-rpm compliment to the primary side, and are used for final “tweaking. does it bog. The secondaries are usually vacuum operated. Holley also has at least a couple 600CFM 4160 series carbs with single fuel inlet, with or w/o electric choke, and with zinc or aluminum bodies. That's why they need some RPM to make the transition smooth. If you have any other questions, feel free to ask. Its a summit stage 2 intake and holley 600 vacuum secondary carb. don't need to wait. I KNOW this is too big. » HOLLEY 750 Double Pumper TIP IN HESITATION Board footera Jump to: FYI Ford, Classic Mustang Tech Discussion MustangSteve Annual Bash Info Paint & Body Tips and How-To's Show Your Mustang Pictures and History Swap Meet Garage Points Ride Height Pictures and Descriptions MustangSteve T-Shirt Sightings Fantastic Craigslist/ebay Finds. The Lean bog I think I can fix with a larger pump squirter and adjusting the vacuum secondary spring to open sooner. 5 inch vacuum. 351C and 600 holley tuning November 21 2002 at 6:14 PM idiot (no login) from IP address 68. dialing in my vacuum secondary holley. Of course I'm running a vacuum can to operate the power brakes and headlights. I was sure that both of these vans were newer than the 72-73 2210's that I already have, and they do have the bowl vent. Next, consider the applica-tion, or how the vehicle will be operated. During the 1960's there were many magazine articles recommending that the ball check be removed and a restrictor / orifice fitting installed. ) will dump more fuel and bog if you stomp the pedal. 040" over) with mild RV type camshaft. The pump is for a quick crowd, like taking off fast. Keep stepping up to a lighter spring until you start to feel the bog, then back off one spring. 050'" transition slot uncovered, 1/16" holes in primary blades. 215cc heads, big solid cam, Weiland intake and a Holley 4160 vacuum operated secondaries. roller XE276 cam, Edelbrock RPM Air Gap, Holley 3310 750 vac secondary and Mallory Hyfire VI-A box). Use a vacuum pump hooked up to the fuel inlet via a 3/8 metal line. Going smaller may eliminate an unresponsive condition normally caused from low vacuum on a BIG cam. If you're determined to use that 750 Holley, you can still get it to run very nicely with some. Runs well, except with the quick snap of the gas to the floor. Ported vacuum does pull an inch or two more vacuum but the vacuum advance is already maxed out at this point so it has no effect on the timing. Since the pump seems functional then I agree that either there's too big a shot initially on tip-in or the secondaries are opening too fast. 5 would have to wait for the vacuum to drop to 3. Think of it this way, accel pumps are battle axe ways to give fuel, jets are precise, PV restrictors are also precise. Go out and pull the hose off the dash pot. When engine vacuum drops to the rating of the power valve the valve opens and allows fuel through the Power Valve Restriction channel in the metering block. Related to your bog. Otherwise, you will get a very bad 'lean bog' when you open the throttles. See our Performance Carburetors, Intake Manifolds, Cylinder Heads, Crate Engines, Electronic Fuel Injection. The carb is a Holley and I was able to narrow the cfm down by the # stamped on it which is 8879. The secondaries are usually vacuum operated. Holley 4150 Secondary Problems I have a 73 Ventura with 400,. there is a cycling of symptoms, first it starts and runs smooth, then acts like it's. Not only does the 770 Avenger probably not flow enough in wet test to actually be an actual 770, but it will not open the secondaries all the way to bog you down, as the vacuum signals will not demand it. It's been 25+ yrs but you should find a recessed screw head on the side top, near the back. Knew it when I put it on there. Drove it a few more miles today, the truck seemed to do it LESS today, but its still "sluggish" it came back down to 650-700rpm today at redlights with the. According to Holley, the power valve rating should be 1+1/2" hg lower than your idle vacuum level. Accelerator Pump cam: varies. I got it for $25, and I bought a Holley Trick Kit to rebuild it. 5 power valve-green accelerator pump cam-. What steps to fine tuning it? (or link to a "how to") Thanks guys. A 285-degree cam may need the “can” to start applying vacuum at 3 to 5 inches with full vacuum advance in at around 10 to 14 inches. When I came in a had a lot of bog in the secondaries of my Holley 750 vacuum sec. Our modern Holley four-barrel carburetor with vacuum operated secondaries (the rear two throats) does this fairly simple. Definitely not too much, as the carburetor will only deliver the CFM the engine demands. easy fix if you know what you're looking for. Secondary opening points have two parts, opening point and opening rate. Called Holley, Jegs tech, and a local speed shop and they all recommended a Holley 750 or 770 Avenger, and they all recommended a vacuum secondary. The air valves are connected by a cam and linkage to the secondary fuel metering rods. If you have any other questions, feel free to ask. I used to get 300+ HP from a 351C with a torque cam and 600 cfm Holley vacuum secondary carb, yet get 19-20 mpg in the highways. My understanding is that vacuum secondaries are best, but I'm not sure if a choke is necessary. It should be two sizes smaller (smaller in vacuum number) than you vacuum reading. See our Performance Carburetors, Intake Manifolds, Cylinder Heads, Crate Engines, Electronic Fuel Injection. If you're running a tight converter and numerically low gears vacuum secondaries hands down. Never forget, it's a MANUAL SECONDARY carb! You can't just stomp on it like a cockroach and expect the same results you get with a vacuum secondary carb. In this case, the larger pump capacity helps the transition. it idles fine and after the bog it runs ok. Its a summit stage 2 intake and holley 600 vacuum secondary carb. The solution is to get a carburetor kit and rebuild the carburetor and test the float. Your secondarys probably don't start to open until 3000 RPM. Otherwise any vacuum secondary carb would never open the secondaries. ZZ502 Vacuum Secondaries not opening. Well, engine is rebuilt in my vette and the rear is now in. I was running a Holley Street Avenger 670cfm on my ZZ4 crate motor until I did a big block swap this winter. Will a double pumper just bog off the line and kill gas mileage? car is a 1982 mustang GT, almost exclusively for street use. But for 1983, Ford stepped up the power to 175 hp, thanks primarily to a Holley 4180 four-barrel carburetor. QUESTION How do I know if a vacuum or mechanical carburetor is best for me? ANSWER For street cars the vacuum secondary carburetor works best on midweight or heavyweight cars with an automatic transmission. There is also a set screw under this that the head points down. I would take the mechanical linkage off of the outboard carbs and get two holley vacuum secondary spring kits and install the small yellow spring in the outboard carbs so they open sooner under vacuum Get them back to stock configuration, but put the a lighter spring in the outboard vacuum pods. A properly tuned Holley, no matter if it's vacuum secondary or double pumper, can be tuned to supply power smoothly and evenly through out both areas, and it pretty easy to do also. These are vacuum-activated valves located in the metering block of the traditional style carburetor. on a light vehicle mechanical secondaries usually provide better performance same logic as a steeper geared vehicle. Going smaller may eliminate an unresponsive condition normally caused from low vacuum on a BIG cam. You might want to look at Holley part number 125-500 Power Valve Check Ball. plus i dont have a stall. 5 power valve and a stiff plain spring on the secondaries. Finished up putting the intake and carb on my '82 today. Holley-type vacuum-secondary carbs are more forgiving compared with mechanically actuated double-pumpers; relatively few vacuum-secondary carb sizes can be made to work on a wide variety of. If there is an off-idle stumble or a bog, you'll need to make. I was taking a carb vacuum actuator apart and a ball dropped out, I found the ball, but is there a small spring missing or do I just put it back with.