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Weber 32/36 Setup, Ch.3

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Assuming you read the introduction in Chapter One and followed the idle circuit setup guide in Chapter Two, it’s time to move on to the primary and secondary circuits.  Again we want to do this in the correct order, as each circuit progressively affects the fuelling, and thus the way the engine runs.  In other words, you want to set the idle circuit up before playing with the primary circuit.  By the same token, you need to dial the primary circuit in before you mess with the secondary circuit.

The DGV series is a progressive two-barrel carburetor, meaning that the primary 32mm butterfly opens first when you move the linkage (or press the accelerator), followed by the secondary 36mm butterfly as you continue to open the throttle.  You can feel the increased resistance when the linkage starts to open the secondary butterfly.  This resistance makes it clear whether you are operating on the primary barrel only or have started to open the secondary.

The primary and secondary circuits are each metered by a main jet and an air corrector, sometimes called an air jet.  The main jet is used to set basic fuel flow volume.  The air corrector is used to adjust that fuel volume as airflow through the venturi increases with increased engine speed and load.  A larger main jet passes more fuel and produces a richer mixture.  In contrast, air correctors (air jets) meter air, rather than fuel; a larger air corrector produces a leaner mixture.

You will have to change these parts in order to achieve the correct air-fuel ratio for your particular engine’s needs and your operating conditions.  The Weber DGV also uses some other calibrated part, such as emulsion tubes, but most street engines do not require that those be changed.  There is also an idle jet on the secondary barrel, but it doesn’t really have much influence and can typically be left alone.

As a reminder, the main jets are inside the float bowl, down at the bottom, toward the rear.  The air correctors are at the top of carburetor body, just behind the float bowl.  Both are located under the the float bowl lid, which covers the top of the entire body.  You will have the float bowl lid off and on several times in the course of changing main jets and air correctors.

That’s enough theory.  Let’s move on to tuning.  The first thing we are going to look at is the primary main jet. This jet typically affects the fuelling from right off idle to halfway through the RPM range that you encounter without getting into the secondary barrel.  Be careful to confine your tuning to low engine speeds only for now.  Higher engine speeds begin to bring the influence of the primary air corrector into play.

A smaller number on the jet indicates a smaller hole drilled through it, and that means less fuel passes through the jet.  In other words, smaller means leaner where main jets are concerned.  Basically, you want to select the smallest (leanest) primary main jet that will run smoothly at low engine speeds on the primary barrel only.  Continue experimenting with leaner primary main jets until the engine bucks or surges at low speeds and low throttle settings, such as cruising slowly around the neighborhood or maneuvering around a parking lot.  Once you encounter bucking or surging, go up one or two sizes on the primary main jet.  Our goal is to keep the air-fuel ratio just rich enough to be smooth and driveable.  Anything richer than that is simply wasted fuel.  We can stay relatively lean here and not put the engine in any danger since it is not under any significant load.

With the primary main jet chosen, you can move on to the primary air corrector, which admits air to emulsify the fuel (mixes it into a froth, more or less) as air velocity through the carb increases.  The air corrector’s influence on the mixture increases as engine speed and airflow increase.  In other words, the main jet sets the base fuel delivery on that barrel, and the air corrector trims the fuel delivery at higher engine speeds.

What you want to do is select the largest (leanest) primary air corrector that will run smoothly through the higher engine speeds when on the primary barrel only.  On the primary, the engine will still not be under massive load, so you can stay fairly lean and still be safe.  Verify that the car will cruise smoothly at high speeds and doesn’t surge, ping, or detonate when climbing hills or using normal acceleration on the primary throttle.  If you’re using a wideband you can look for air-fuel ratios around stoichiometric, somewhere between 14.5:1 and 15.5:1 at steady cruise, and 13.5:1 or 14.0:1 under light acceleration and moderate load.

At this point, the vehicle should be smooth and responsive on the primary barrel under any conditions. Once the primary side is sorted you can address the secondary, but the primary side MUST be sorted first.

Moving on, the secondary circuit is calibrated in much the same way as the primary, but it’s important to remember how the secondary side of the carburetor is used.  Most normal driving is done on the primary barrel, with the secondary being opened only for heavy loads or maximum acceleration.  For that reason you’re going to want progressively richer air-fuel ratios when the secondary is open then you would when driving on the primary barrel only.

Secondary tuning also starts with the main jet.  This time choose the smallest* size secondary main jet that provides smooth performance as the secondary starts to open, and midway through the RPM band, with the secondary barrel open. This is a good time to start paying attention to the wideband, if you have it, to monitor the air-fuel ratio.  If the secondary is open, you generally want to see an air-fuel ratio between 12.5:1 and 13:1, going richer as speeds and loads increase.  If you do not have access to a wideband oxygen sensor and air-fuel ratio gauge, proceed very carefully through leaner secondary main jets.  At the first sign of surging, hesitation, detonation or pinging, go back up at least two sizes richer on the secondary main jet.

Finally, take a look at the secondary air corrector and choose the largest* size that provides smooth performance through the upper portion of the RPM range with the secondary throttle open.  Be aware that we are now deep into a potential minefield.  It is entirely possible to destroy your engine if you run it too lean under heavy load.  Buying or borrowing a wideband oxygen sensor is practically mandatory if you want to establish the correct air-fuel mixture.  As you did with the secondary main jet, go back at least two sizes richer (smaller number) on the secondary air corrector if you experience any surging, hesitation, detonation or pinging in the RPM and load band we are testing in.

*Please understand that tuning for WOT (wide open throttle) air-fuel ratios without a wideband oxygen sensor and air-fuel ratio gauge is very risky.  In the days of leaded fuel, you could read the spark plugs to get an idea of how rich or lean the engine was, but that’s much tougher with unleaded gas.  If you cannot afford to buy a wideband system, consider borrowing or renting one from a friend.

And there you have it – DGV tuning step by step.  Not exactly cutting-edge technology, but sometimes it’s worthwhile to revisit things, and these are still popular and viable carburetors on a whole lot of older cars.  Have fun and be safe!


  • My BMW 2002 engine been completely rebuilt with Schrick 284 and new 32/36 DGAV. Very difficult when first start in the morning and took more than 5 minutes to idle and sometime experience dieseling when shut off. The jetting is factory standard. What seems to be the problem. Thanks

    • Thanks for the inquiry. Your problems could be caused by any number of issues, or a combination. You’ll need to find a local mechanic with carburetor experience to perform some hands-on, tools-on diagnosis.

  • I have a question on 32 36 dfev 1600 vw super beetle.
    First how do you adjust secondary throttle plate with screw stop? I am down to a 120 p
    main 170 air 50 idle jets and still runs rich?

  • Hello SV3Power. I’ve installed a 32/36 on a 250 Falcon engine and you mentioned above the same carb was fitted to a Jeep 258 engine. DO you have any idea what jets and tubes were fitted on that application? I’ve been very pleased with the 32/36 but since rebuilding the motor it’s never been the same. Any advice would be great. Thanks………….John.

    • Hi John,

      The 32/36 is intended for an engine about half the size of your 250. Your engine is so large that the butterfly must be open quite a bit just to get enough air to idle. Opening the butterfly so far exposes the progression holes to manifold vacuum, which usually means a very rich idle and a lean stumble when you open the throttle.

      You might try drilling a hole in the primary butterfly to allow airflow into the engine without opening the butterfly so far. Start with a small hole, maybe 1/16″ or 1.5mm, and go up from there. Take a look at some of the books mentioned in other comments to see where the butterfly should be in the idle position.

      The ideal solution is to get rid of the toy carburetor and go back to one designed for a large engine.

  • Hi,
    Great write up and a massive thanks for sharing the information. Even finding a rolling road that truly knows what they’re doing is getting hard here now.

    One question on carb choice; for a 2.0 16v 126bhp (a honda b20b low compression) engine will a 32/36 do the job?

    I’m looking at a 32/36 DGV and a 38/38 DGS.
    I’m not looking to tune it beyond standard but the exhaust system will be very short due to the engine location in the conversion.

    • Hi Ivan,

      Glad you enjoyed the article! I am not actually a fan of these carburetors, and I wrote this article mostly because so many people don’t know where to start with them. My preference would be to stick with your engine’s original fuel injection if possible. It is superior in every way to a single carburetor. If EFI is just not an option, my first choice for carburetors would be a set of secondhand motorcycle carbs; second choice would be a pair of refurbished SU HIF6 or HIF44. None of these are as simple to tune as a single DGV, but the response and power would be significantly better.

      If you absolutely must use a single downdraft Weber carburetor, a 32/36 will probably be adequate, but no more, so I’d probably opt for the 38/38.

      • Where im putting the engine means I can’t use the original honda efi due to the distributor location. I had been looking at aftermarket management but the cost is fairly high especially once the fuel system has been upgraded (the car was originally carbd) and the mapping is done. Nothing is ruled out though.

        I actually think I have a pair of hif44s that I could use but the problem is that getting someone who knows what they are doing with them is even harder than with the weber. I dont think they lend themselves very well to trial and error tuning with a wideband.

        Still though, excellent food for thought. Thanks.

        • Fair points. You might look into MegaSquirt. Even a basic MS1 on a V3.0 board will happily run EFI on a simple four-cylinder, and it is easy to set it up with crank trigger ignition, such as the Ford EDIS trigger wheel and coil pack I use on my Toyota 4AGE. That would eliminate the distributor and possibly free up some room. Overall cost is very reasonable.

  • I have a new 32/36 electric choke on a BMW 2002.
    The primary starts out ok but seems to run out of steam and bumbles at 2500-3000
    If I depress the accellerator into the secondary it has power but the transition isnt smoothe.
    I have been sent some jets from fred at weber in New york. It had 140 in both jets inside the bowl.
    Are they for both primary and secondary?
    I see the other jets on top but he didnt send those just some other jets that look like larger idle jets.

    • John, thanks for the question. It’s not really possible to tell you over the internet what jets will make your car run best, but the fact that it runs OK on the primary until the RPM climbs indicates that you may need to try a different air corrector on the primary side. Air correctors are the larger jets you can see looking straight down into the air horn.

      If you have access to a wideband air/fuel ratio sensor, use it! A wideband setup takes most of the guesswork out of the equation. You must still have a solid understanding of the appropriate air/fuel ratio for each condition as well as understand how making changes to the carburetor affects the air/fuel ratio.

      I suggest that you read the entire article here (all three chapters), front to back, before beginning any work. If you follow the directions listed, and perform each step in the suggested order, you can get it running well. Work methodically, changing only one thing at a time. Note your changes and what effect each change has.

  • Hello. I have a 32/36 and found this miles ahead of all other explanations out there of how to jet one of these properly. I would like to know if I could post this as a tech write-up on YotaTech.com. I know A LOT of people on there will find this useful. Thanks!

  • Much more clear than most on the subject. Thanks.

    I would love to see an advanced discussion of the relationship between main, AC, and tubes to balance the “tilt” of AFR through the range and maybe relationship to float level. All I find is “Advanced, probably OK”

    I see two trends, large idle, small main and small idle, large main. Both can get a base AFR, but which transitions better?

    I also see comments “secondaries are usually one size smaller” but no discussion of why.

  • How important is a fuel pressure regulator for a DGV? I’m running mine on an MG midget with a Carter fuel pump.

    • I’m not sure, but I don’t believe DGVs are as sensitive as DCOEs, IDAs, etc. You might contact Weber or Redline, and/or do some more searching around the web. Some fuel pumps are low-pressure units that work fine with those carbs that require low fuel pressure.

  • you wouldn’t believe how long i’ve searched the net for this information…really informative and easy to understand…The penny has finally dropped! Cheers

    • Thank you for stopping by! Good luck in setting your Weber up. Watch out for throttle shaft and housing wear, too. These carbs aren’t built to take the same use and abuse as the old DCOE, IDA, etc., and don’t last forever.

  • Have a 1980 TOYOTA 4×4 pickup w/20r Weber 32/36 DGAV carb on an Edelbrock dual port manifold. Doing complete overhaul, boring .020 over, cleaned up the ports to match gasket. Printed this out so that things don’t get lost between the computer and the truck. The tuning tips appear to be pointing me in the right direction. The carb now is as it came out of the box.

  • Thank you so much for actually putting a logical, informative article about tuning these carbs on the internet! And especially thank you for including what to look for with the wideband AFR. It is REALLY hard to get any good info on a methodology behind tuning these carbs using an AFR. Considering It’s my first time with tuning carburetors (I’m used to FI) I can’t imagine why you wouldn’t use one. You guys rock!

    • Glad to hear you liked the article. Using a wideband sensor definitely makes things easier, especially considering how affordable and available they have become.

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