For more tuning information, see http://www.1800vw.bizhosting.com/progcarbtune.htm.
When you order a Weber Progressive for your air-cooled motor you are never quite sure what the jetting will be. Over the years various changes have been made to the main and air correction jets without any real plan from a sellers point of view. The Progressive in its various models have been used on over 100 models of cars and trucks, foreign and domestic, in factory and aftermarket applications. Also the type of Progressive you may receive might be different from the one you ordered or expected to get.
The linkage setups for air-cooled VW work on both the DFAV/DGAV and the DFEV/DGEV carbs. The "E" is for electric choke and the "A" is for water choke. Make sure you get an electric choke as hot water is hard to come by in an air-cooled vehicle. The DGEV is the mirror of the DFEV and have been used successfully in dual carb setups for 2500 cc and above type IV and Porsche engines although the response is not as snappy as other types of dual carbs. If you have an application for dual 48's then dual Progressives might be a little more streetable. The DGEV come with a solenoid fuel shut off valve just like your original Solex, but you will need to lengthen the solenoid wire to reach the front mounted cutoff on the Progressive.
The first carb I took apart had the following jet setup:
The major problems when installing the Progressive carb are due to dirt and air leaks and debris in the intake runners. In the past it was possible to find that the intake manifold runners were too long. Today you may still find that situation when the crankcase cylinder faces have been surfaced or the heads fly-cut to raise the compression. This will narrow the engine causing an excessive runner length. Make sure that when the intake castings are bolted down that the center section is still loose in the boots. It is an excellent policy to always check the runners for dirt and debris. Some of the center sections come with the heat risers molded in place and others you have to assemble. Still other makes of intake center sections have no provision for heat risers at all. Make sure that your application is correct for the type of intake you get. The majority of uses are for street vehicles and will require the heat riser. This is a heavy carb and manifold so you need to install a bracket to take some of the strain.
If you suspect dirt in the carb, even if it is brand new, there is a little trick you can try prior to tearing it down. This is how it happens. Dirt will build up over a time in your fuel lines and even new lines will have some residue. When the lines are wiggled while changing carbs or fuel filters, some of this will break loose and flow into the carb. A trick to break loose this dirt is to rev up your engine and then slap your hand over the top of the carb creating a huge vacuum. This will usually suck the dirt right through. The hard stuff that is still lodged in the fuel circuit will necessitate tearing down the carb regardless.
During the adjustment and re-jetting process you will want to have a spark plug color chart to check where your burn is and decide which direction to go. You can usually pick these up at the auto parts store or there may be one in your repair manual. These are good to see where you are at in the process. I found a good color chart in an old Clymer's shop manual for a different vehicle. It will work fine for this.
As a baseline you will want your motor to be in peak adjustment. That means the distributor timing is set, the points and plugs are gapped properly, and the valves are adjusted. If you are running larger aftermarket heads and have some intake porting, it is suggested to get the larger diameter intake manifold end castings available through many of the VW parts suppliers listed in the VW mags.
Carb adjustment starts out with your float setting in your float bowl. I am like you, I'd rather not take the carb apart first, just use it out of the box with some minor exterior adjustments. The float setting is critical to everything else and must be checked. Floats can be out of whack from poor manufacture or remanufacture to just being jostled during shipping. You need to know where it is before changing anything else. Do the next step before installing on the engine.
The top and bottom surface of the float must be parallel to the gasket surface of the float bowl. To check the bottom surface of the float you need to hold the carb upside down at about 45 degrees (this keeps the weight of the float from compressing the small spring in the float needle). The gasket surface to the bottom surface of the float should be about 1.5" or 38.5mm.
I like to set up this carb on an engine start up stand in order to get to all the hard to reach places, most of you do not have this luxury. Before changing jets you need to check out the low speed settings as they will affect your motor from idle to over 3000 RPM. Back out the idle screw (it's the one on the linkage on the left side of the carb). Then screw it in until it just starts to move the primary butterfly (be sure the choke is full open and place your finger on the butterfly to tell when it first starts moving). Then turn it ONE FULL TURN.
Next item is to set the idle richness screw -- that's the one below the choke on the front of the carb that's impossible to get to. This screw controls the amount of pre-mixed air and fuel. Screw it all the way and lightly bottom it out. Then back it out two (2) turns. I use a real short fat handled screw driver to get to this beast.
The factory VW fuel pump will handle the supply to this carb under all but the most strenuous running. On dune buggies and vehicles that really wind up you will need to install an electric fuel pump and a fuel pressure regulator. I set the regulator to halfway for the base install. Now start the motor and let it warm up without changing the screw setting. Once the motor is warmed up and the choke has fully rotated, screw the idle richness screw in or out until you hit the highest RPM.
Next, after letting your motor cool you must check how many turns out the idle richness screw is. Be very careful not to bottom out the screw hard when you do this. If the idle jet is the correct size you will be 1 3/4 to 2 1/4 turns. If you are less than 1 3/4 turns out, install a smaller idle jet and if it's more than 2 1/4 turns out you need to install a larger idle jet. The only idle jet we will change in this article is in the primary circuit as the secondary jet (140-145) is large enough to handle the demand when the secondary is engaged.
If you had to change the idle jet (the one on the left of the choke element) then go back and adjust the idle mixture screw again until you end up with it out about two turns for the highest RPM. You may want to turn it out another 1/2 turn to richen up the idle to compensate for low end drop out when the accelerator is pressed.
Now that the low speed circuit is properly adjusted you can now use your spark plug color chart for adjusting the main and air correction jets.
The backyard method, but one that works well, is to slowly run your engine up to 3500 RPM while attached to your tach and view the main jet in the venturi. It should start dripping fuel at this RPM into the throat of the venturi. If the fuel starts dripping at a much higher RPM then increase your main jet. If fuel starts dripping at a lower RPM than 3500 then decrease the size of your main jet. An engine installed in a Beetle or bus will force you to use a light and mirror to see this. Not everyone has an engine start up stand. I use an explosion proof sealed fluorescent shop light in the engine compartment.
Although some low end throttle response can be helped through more initial spark advance, be careful where you set your timing. Too much advance too soon can be sure death to your motor. You don't want your advance all in before you hit your cruising RPM.
You will notice that the air correction jets were never mentioned. The carb comes with all the air correction needed for any engine jetting from 1600 cc to 1904 cc. Your mixture setting and main jet size is what is important on this carb.
For my specific use on an 1835 cc engine with 041 39 X 35 valves, a 009 distributor, and a stage 2 cam I came up with the following setting:
It's a hassle to set up and time consuming. That's why a lot of people give up and say that the Progressive is useless for VW application. Like all carbs, they have to be set up to match your engine size, but when dialed in, will perform satisfactory and give good mileage at the same time. You have the extra benefit of being able to stomp on it when you want to play and have extra umph available for that race to the stop light or passing on the highway.
Information from the DBG web site: http://www.dreamwater.com/dbg/how_do_you_run_a_weber_progressi.htm
"How do you run a Weber progressive with a vacuum advance distributor?
There is a small vacuum port on the progressive, but left alone it produces way too little vacuum to be of any help. There is a fix however. The way we did it was this:
Method 1) with the stock carb or FI system read vacuum at the stock port with your mini-mightymax vacuum pump and tester. Take this reading at the RPM where your distributor is at max advance (on the test engine it was at 3100 RPM). Now install the carb and read the vacuum at the same RPM. Enlarge the port using a selection of long and really tiny bits until the readings match the stock set-up.
Method 2) Determine what RPM you want full advance, this may not be as easy as it seems. Then hook-up the pump to the diaphragm and start pumping until the dizzy is at full advance. Then start enlarging the port on the carb until you get the right vacuum at your revs.
Some notes: Drilling the vacuum port voids any thought of a warranty on your carb.
The port is at the point of tightest restriction in the carb throat. It can be tough drilling and not damaging the carb. To do so, you will need to remove the brass vacuum port fitting and attack from the outside using a selection of jetting bits. Be really sure to clean shavings after every drill.
The vacuum level may rise quickly depending on how well your engine breaths. The larger the engine the more vacuum you will have. Once you set your vacuum level, mark your carb in some manner to signify that the vac port diameter has changed.
Be sure you're done with improvements to your motor before you do this. Better breathing motors cause larger vacuums at lower RPM's, your dizzy may start to advance too quickly if you did the carb before you install 1.25:1 rockers, bigger cam, larger jugs, etc.
Take your time. It took us 3 days to get mine just right."
Here are a few things I learned from the Redline site: http://www.redlineweber.com/html/application_guide/making_the_right_choice_32.htm DGV and DFV are essentially mirror image carbs. The throttle primary throttle plate rotates clockwise in the DFV series. We use the DFV series on the VW Beetle (DFEV).
The E in DFEV is for Electric choke. The A in DFAV (or DGAV) is for water choke (aqua? Weber is an Italian company.)
DGV series carbs are available with an Integrated Cutoff Valve (ICU). This is the same as the electric idle solenoid on stock VW Solex carbs and prevents dieseling or run-on after you cut off the ignition. I do not know if the ICU is available on the DFV series carbs.
The DGV series is available as a non-progressive, synchronous opening carburetor. This is a two barrel carb where both throttle plates open at the same time. These carbs are the 38 (mm) DGAS and 38 (mm) DPS. Redline recommends this carb for modified engines (hotter cam, headers, larger engine size, and presumably high flow cylinder heads). There does not appear to be a corresponding DFS, so those of us running VW's would have to do some interesting throttle cable modifications to use the DGS. I cannot tell if the DGS is available with electric choke (I guess it would be called a DGES). Of course, if you want a two barrel synchronous carb, the IDF is a better choice at about the same price.