Mechanical & Vacuum Secondary Holley VS Carter/Edelbrock, Rochester Velocity Style Carburetors

more carburetor stuff so every time we do one of these carburetor videos we always get really good feedback you know the fundamental videos so we're going to continue the last one we did was on carburetor sizing now the formulas don't always add up the real world results this time around I want to talk about the different styles of carbon the ones that we commonly come across so obviously I can't cover the entire history of the carburetor in every type of carburetor there is I'm going to focus only on the type that we commonly use the type that we commonly come across on types of cars and the types of builds that we do and it's important to note here that every carburetor that's currently in common is 4L carburetor is a derivative of one of these so it's all going to fit the only one isn't really represented here is is the summit style which is an auto like carburetor that was revamped by Holley and now it's marketed by Summit and essentially it's the same as a vacuum secondary Holley roll intents and purposes functions the same so we're going to run through the evolution here and talk about the differences between mechanical secondary vacuum secondary and velocity secondary carburetors so you're talking about vacuum and mechanical and all these cars have mechanical carburetors these carburetors all have mechanically operated secondaries but they all have a delay feature built into them and we're going to get to that in a minute but when you're talking about mechanical and vacuum is pretty much strictly talking about Hollies now all of these carbureted designs date back to the 1950s and early 1960s and everything's just an evolutionary step from there and the evolution really ended right here with the thermal quad but that's what I'm getting ahead of myself let's let's start from start so the most simple basic straightforward type of Four Bell carbonator is is known as a double pumper right and what a double pumper is is very simply this is a double proper carburetor it means it has an accelerator pump on the primary side and an accelerator pump on the secondary side there's a direct link between your foot and the function of the secondaries now let's talk about accelerator pumps for a minute just just the people who aren't familiar it's important to note that all of these carburetors have essentially the same exact function on the primary side the primary side is where your idling is done the primary side has a direct one-to-one relationship with your foot with the gas pedal the throttle and each of these has an accelerator pump all different styles of accelerator pump but accelerator pump on the primary side or the accelerator pump does is simply fill in the void between the time you open the throttle and velocity through the carburetor is able to pick up and suck fuel out of the boosters so if you didn't have an accelerator pump you'd step on the gas and would just go buck and die right because you first open a throttle so you're idling your your vacuum is high you're pulling fuel through the idle circuitry you open the throttle that vacuum Falls away and before fuel can be pulled through the booster as the engine will die the accelerator pump just squirts raw fuel into the carburetor to make up for that little Gap so the primary side of all of these carburetors is functionally identical they're all different styles but functionally identical the double pumper Holley is literally two two barrel carburetors back to back so essentially you've got two primary sides and they're just one face at the front one faces the back in one package and there's your double pumper Holley the vacuum secondary so remember we need a delay from the time the throttle the throttle blades are open and the time the fuel is going to be pulled through the booster there needs to be a little a little bit of a delay there you can either delay it or you can add supplemental fuel the double pumper has the accelerator pump over the secondary side the vacuum secondary has no accelerator pump over the secondary side so what they do with the vacuum secondary is delay the opening of the the secondary side of the carburetor until there's sufficient velocity through the primary side to ensure there won't be a flat spot or a bog when the secondaries are open no secondary accelerator pump just keep the throttle blades closed until there's enough air coming through the primary side that it can support the opening of the secondary side it's that simple so velocity through the primary side is translated into vacuum there's a vacuum passage that goes from the primary side to the secondary diaphragm and then when a sufficient velocity through the primary side the secondary starts to open that vacuum has to fight a spring that's in here and that's how you tune the secondary side of the carburetor if you were to put too light of a spring in the secondary side it would act just like a mechanical secondary carburetor with a bad accelerator pump on the secondary it would just it would die so that's the whole purpose and function of a vacuum secondary carburetor and this is the summit carb which by the way is a fantastic carburetor I was surprised when the first time I used one is functionally the same as actually the vacuum the vacuum diaphragm on this carburetor is directly from one of those Summit carburetors so they're that interchangeable and they're fantastic pieces so that's your essential Hollies and all 100 of your derivative Holley carburetors anything that this how many different companies make Holly clones or Holly knockoffs are all based on one of those two style carburetors all right so now we're going back to the 1950s because that's when these these styles of carburetor were first developed previous study everything was a two barrel so there were a couple different versions of four barrels early crude four barrels at the time and one of the best of them in the The Hollies came around in 1956 or 1957. just previous to that Carter carburetor company started making four barrels and they came out with the wcfb that was the original Carter four barrel carburetor so what does wcfb stand for William Carter four barrel that's it that simple there's no there's no magic designation to wcfb and that was the original Carter version of the four barrel carburetor one of the issues that they were having even back then was vapor lock and heat silk it's just a universal problem with dealing with gasoline and the materials that they're made of like for instance The Hollies are not made from aluminum the wcfb was also not made from aluminum it was subject to a heat silk issue so in order to beat that heat silk issue they revised the carburetor completely and came out with this and this is this is an Edelbrock version of it and the Edelbrock is just a clone of the Carter AFB so what does AFB stand for aluminum four barrel that's it that's what AFB means wcfb Will Carter four barrel AFB aluminum four barrel and the whole purpose of making this thing out of aluminum was so it would dissipate heat and be less subject to Vapor Lock and Heats and heat soak than these other types of carburetors aluminum four barrel so the AFB differs from the Holly in that while the secondaries are linked mechanically mechanical secondary just like the Holley the Holley mechanical secondary is there is no secondary accelerator pump or any way to delay the actual opening of the throttle blades so what Carter did is it Incorporated wait but I just got to explain this carburetor real quick this is an example of how you can get burned in a swap meet real easy I bought this thing I don't know eight or ten years ago at a swap meet it looked it looked pristine and I got 100 bucks for it so I was like well I need one here I'll take that so when I got it home I bolted on the car car went wrong what's going on with this thing so I popped it apart and found it it was a flood carburetor we had a massive flood here in Nashville a year or two before I bought this carburetor and this thing had been sitting with water in it just just rotting away for that's not from gasoline that's from water so uh it's it's it's trashed the uh the Jets are actually kind of like corroded into the body of the car whether it's not useful for anything except parts but that's how you get burned me it could look pretty but you never know what's on the inside of them so the AFB mechanical secondaries right so the secondary is linked to the primary side there's no vacuum operation there what they did was They delayed the air through the boosters by using this weighted air door so what this does is these weights hold this close hold these butterflies closed until the sufficient velocity through the secondary side of the carburetor so that it overcomes these weights and these doors open these little notches here are there to direct the initial shot of of air coming through the initial vacuum of the initial pull from the engine to the underneath of the booster and start the booster flowing and then once the booster is flowing and this only takes really an instance like a like a fraction of a second velocity picks up enough it overcomes the weight these weights and poof the slops open and you have four wide open barrels the downside of this is that this is a restriction in the second it this is this is a flow killer because it's just I remember when these things were designed flow wasn't really a problem you know it wasn't a consideration this carburetor design is from 1960 so you're still feeling very small engines you weren't moving a lot of air through these things so a little bit of restriction from the secondary air valve in there didn't really end up but it's one of the reasons why Hollies for ultimate performance have a big advantage over the Carter edelbroxtol carburetor so and there was another thing too there was a there was a tuning trick to these so people used to put the biggest Carters they could on small engines back then 283 Chevys and 260 Fords and 273 Mopars they wanted a lot of carburetor but couldn't handle a bunch of carburetor you know initial punch so what they would do is actually add weights they would they would drill they would drill into these and add lead shot they would do all kinds of modifications to the to the counterweight on the air door to delay that opening enough for the engine to get up you know up on a pulling velocity to keep these things closed and keep it from bogging so you were able to use 625 CFM Carters afbs on Tiny engines I not have a box that was the big tuning thing with these adding weights playing with the counterweights so that's that style carburetor now the odd one out here we've got Howies we've got Carter edelbrocks the odd carburetor out here is the Quadrajet and the Quadrajet is important because this was the next step in the evolution of the carburetor these were introduced in 1965 1966 and instead of having again in these are these are mechanical secondaries it's a direct linkage between the primary and the secondary side of the carburetor but instead of having a weighted air door they use a velocity operated spring-loaded air door so spring pressure instead of weight keeps these is is the resistance the delay factor in the secondary side of the Quadrajet they also operate with a vacuum brake to keep to again delay the opening of the secondaries until just the right time the advantage to this is that you don't have it's it's not the same uh detriment flow that the air valve second or the uh the weighted air door has so this was the next step in the evolution of this style carburetor the 1968 Carter says well Rochester has a better system for the secondaries than we have so what they did is they revised very slightly the AFB and came up with the ABS so the AVS as you can see has this air door this air valve exactly the same as the Quadrajet and the AVS so what does AVS stand for air valve secondary Carter just through these letter combinations you know there's no continuity between but anyway yeah so aluminum four barrel and then air valve secondary that's that's what those abbreviations mean so functionally it's the same as a AFB Edelbrock style carburetor and now Edelbrock makes these things also the Edelbrock abs's is there a real difference between them you will never find it the the only real advantage that the AVS has over the AFB is the tunability of the secondary air door secondary air valve because you can type because it's spring-loaded you can tighten and you can adjust it to get it to get it where you want it to be from Maximum hit where you can okay you can you can add and take weight off the air doors on an AFB but it's much more difficult than just turning the spring and and tightening and loosening the tension on these and then what I would consider to be the last step in the evolution of the common four barrel carburetor that would be 1968 when Carter introduced the thermo quad as direct competition for the Quadrajet and this also incorporates just like the Quadrajet incorporates a secondary air door a spring operated secondary air door with a vacuum brake to delay the opening the main functional difference between these two carburetors is that the air door on the Quadrajet Works to pull up the Jets on the secondary side where there's no relation to the Jets on the air door on a thermal quadrant so that's pretty much the evolution and the essential differences between the types of carburetors that you're going to come across the mechanical vacuum and velocity style secondary carburetors all of the main differences of course each of these carburetors is completely different in there in their construction but the concepts are all the same the primary side is always one to one always has an accelerator pump always has idle circuitry and so on and so forth and then these when you get to these velocity style carburetors big differences in the function of the secondaries but again the whole purpose of it the only reason these these differences in the secondary side of the cargo to resist at all is just to compensate for that that black flat punch it and the secondaries were opened to compensate for that lack of velocity through the through the carburetor itself that'll pull fuel from the boosters that's the only reason these differences exist which one is going to work for you just depends on what you're expecting to get out of your car and what your tuning abilities are what your tuning desire is any one of these carburetors will function for a typical car typical circumstances any one of these style carburetors will function just fine the engineers knew what they were doing when they built these things so that's it for now and I hope you got something out of that I'll see you tomorrow

Channel: Uncle Tony's Garage

Views: 51,487

Keywords: should i go with holley or edelbrock, edelbrock metering rods, holley or edelbrock, holley vs edelbrock, edelbrock carb adjustment basics, edelbrock performer carb, edelbrock vs carter, edelbrock rebuild kit, edelbrock calibration kit, edelbrock jets, edelbrock carb, edelbrock avs, off road needle and seat, edelbrock avs2, ethanol damage, edelbrock tuning guide, holley carb, edelbrock 1406, holley carb adjustment basics, edelbrock, carter competition series, big block mopar

Id: -avtcub3W6o

Length: 16min 43sec (1003 seconds)

Published: Mon Oct 10 2022