Carburetors can make a big difference in how your auto performs. The stock setup when set up properly with heat does an adequate job under most conditions. But as these carburetors age and become neglected, performance suffers.
For those desiring more performance from their stock engines or wish to run performance engines, then a carburetor upgrade is in order.
Most carburetors used on VWs come in either single barrel (bbl) or double bbl and can either be used as a single setup or as a dual setup. Although just about any carburetor can be grafted onto an VW engine, the following are the more common setups seen on aircooled VWs.
VW Carb Choices
Centermount Single Barrel
Weber single barrel (used back in the day)
Centermount Double Barrel
Weber Progressive DCAV (water choke) or DCEV (electric choke)
Weber IDF or DCNF
Holley BugSpray (older carb - generally worn out)
Dual Single Barrel
Dual Double Barrel
Weber DCNF (obsolete)
Solex 40P11 (Porsches)
Single Carburetor Setup
For single setups, heated manifolds are a must. Without manifold heat, the carbs will "Ice" and fuel will dribble down the intake manifold and pool. This icing will make it impossible to drive. When it comes to manifold heat, the amount of heat delivered to the manifolds varies greatly by design. Some manifolds don't allow for heat, others have heat tubes that pass through the bottom of the manifold and the best ones allow for heat to pass through the main body of the manifold. Because of this, you will need an exhaust that allows for manifold heat and these system will not work on Type 3 and Type 4 VWs without significant fabrications to allow for heat to the manifolds. The economy heated manifolds that allow heat to just pass through the bottom of the manifold will benefit from preheating from a block heater in the winter - but this is just crazy.
Heated air routed from the outside of the exhaust tubes or from underside of the the cooling fins on the heads into the intakes can also help prevent icing and increase burn efficiency.
For offroad use, many drivers prefer a single carburetor setup over duals as there is less linkage to get buggered up, having a single carburetor to deal with is simpler than having two and because a single carb and intake can be set inboard away from the dust cloud, mud, water and rocks being thrown from the rear tires.
From the factory, these worked well and allow a stock engine to run smoothly. But over time, many of these have worn out and no longer work well. Failure of the stock carburetors are often the result of vacuum leaks such as from a worn throttle shaft bushing or just because the carburetor is filthy and in need of a good cleaning. New carburetors are still available and quality machine shops such as RIMCO can repair and restore most stock carburetors. But carburetors such as the 34 PICT are difficult to rebuild and you may have better results replacing them.
Comparing stock Solex carbs to each other, and to the H30/31
The VW Carburettor
The Solex 30/31 can be used as a stock replacement, but needs a main jet change for this to work properly. Some of these were poorly made and may not work, even if new.
Progressive Weber DCEV
These use a small primary barrel which allows for reasonable drivability and fuel economy and a larger secondary barrel that opens up at increased throttle. These carburetors are not set up properly from the factory and will need to be appropriately jetted for your VW application. This can be difficult and time consuming as the factory jets and adjustment is difficult to get to. Quality kits sold by VW specialty shops may set these up so that they are in the ball park, but you will still need to spend some time getting everything set up.
A progressive Weber can be a real bitch to setup just right, but once dialed in on a heater manifold - it can work quite well. It will not work without a heated manifold and will only work in warm weather with a low quality heated manifold. This setup must have heat o work!
The linkage also differs from kit to kit. The factory Weber linkage will not allow for full wide open throttle without modifying the accelerator. The Redline kit has the proper linkage for a VW and a fully heated manifold to allow this carburetion system to work even at lower temperatures.
More information is available on the Weber Progressive Page.
A single Weber IDF is also an option for Baja drivers looking for something less complex than a dual setup. IDFs come in 40, 44, and 48mm sizes and many feel that these are the ideal setup for offroad racing.
More information is available on the Weber IDF Page.
Dual Carburetor Setups
With these setups, air and gas basically drop right down into the intake valves of the engine. There really isn't enough time or distance or the aerosolized fuel to condense and pool like with center mount setups. This alleviates the problem of icing and can make metering of fuel into your engine a little easier and less restrictive. Duals are therefore far better suited for winter driving than center mount system.
These setups do require more linkage and synchronization of the carburetor setups for optimal performance. This does increase the complexity of the setup as a whole, but most agree that the benefits of a dual setup well outweigh the drawbacks of increase complexity that is part of dual setups.
In regards to the dual carburetor manifolds, aluminum is much more desirable than steel manifolds. Besides aluminum being lighter than steel, it heats up much faster than steel which helps keep the fuel headed for the spark plugs warm and vaporized.
Dual Carburetion Linkage
The linkage used for dual setups and often be the source of problems with your system. They come in two general types - centerpull and crossbar linkage.
The centerpull linkage have a pivot point in the center of the engine that pushes or pulls the carburetor throttles open.
The crossbar linkage system uses a crossbar over the carburetors to push the throttles open
When an aircooled VW engine heats up it expands and the distance from the individual carburetors in a dual carburetor system increases. If you have a centerpull linkage setup, the throttle position can be affected by engine temperature which can cause a variable idle and make it difficult to tune your carburetors. Crossbar linkage systems are far less affected by engine temperatures.
Linkage can also be made from aluminum or stainless steel. Steel is generally more durable and less problematic than aluminum for this application.
Dual 35mm Solex
A popular and economical dual carburetion system for dual port upright engines uses dual 35 mm Solex carburetors. These kits offer a small amount of increased performance over the stock single carburetor system and don't require a tremendous amount of maintenance.
Aircooled.net has a popular kit with a modified linkage setup and factory intake manifolds and carbs.
Kadron are Brazilian made Solex carburetors. They are great carburetors for what they are but have very a poorly designed center pivot linkage system. The linkage is notorious for failing, but since these systems are so economical, they have a popular following.
Dual Bus Solex
These carburetors work well but don't really provide much of a power increase over the stock carb. These also have a center pull linkages system and are very difficult to work on.
This is an old and obsolete carburetor that was widely used in the past. These were good carbs, but flood easily and should not be used for offroad applications.
Dual Weber IDFs
This is probably the most popular dual setup for VWs. These one in 40, 44 and 48 sizes and work very well when properly sized and jetted for your particular application. They fit the engine compartment, have a modern float design that is less likely to flood and they have provisions for a vacuum advance.
More information is available on the Weber IDF Page.
Dual Dellorto DRLA
Dellorto DRLA are great carbs and very similar to a Weber IDFvs. Unfortunately, it can be difficult to find and very expensive to find parts for it. Because of the cost factor, these past the the practicality test of most VWers - who are often cheapskates by nature.
One should note that the sizing of the Dellortos is different than the sizing of Weber carbs. A 36mm Dellorto is more or less equivalent to a 40 mm Weber a 45mm Dellorto is equivalent to a 48mm Weber and so on.
Dual Weber IDA
Weber IDAs are race carburetors that are either idle or full throttle and don't have much of a progression circuit in an unmodified form. They can be modified to work well for street use and efficiency ranges from anywhere between 8 and 27 MPG, depending on jetting.
IDAs are not setup with a vacuum port appropriate for vacuum advance distributors.
Aircooled.net Tech Articles
If you aren't afraid of a little technology, then fuel injection is great once it is set up.
Several companies make "bolt on" systems that will fit a VW. These may require a bit of drilling, welding of the O2 sensor and setup of a second fuel line. The downside of these setups is the high initial cost and the fear of technology.
There is also a following of DIYers who put together their own setups. This will require a secondary fuel line, electric pump, pressure regulator, O2 sensor (generally), throttle body, throttle body sensor, injectors, a computer and a good deal of imagination, understanding of fuel injection and fabrication skills. There are also DIY kits to make this much easier and MegaSquirt has made it much easier for the DIYer looking for the ultimate fuel management system.
More information on this can be found on our Fuel Injection Page.
Turbo and Superchargers
For those looking for a lot more power and not willing to just get a non-aircooled engine or an entirely different auto altogether, turbo or supercharging is an option. This can require a buildup of the entire drive train and a good amount of fabrication and/or share cash for a proper setup.
Converting your VW into an Electric Vehicle has become popular over the last several years. Information and discussion on this can be found on our Electric Vehicle Page.
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