Weber Conversion

Build a Weber 32/36 single progressive carb conversion for your air-cooled VW using junk yard parts.

This is a copy of a copy of a page I wrote in the late '90s describing the steps undertaken, the parts bought and the end results of a project to convert my ageing Volkswagen camper motor (1.7l, type IV) from its original dual Solex carb setup to a single progressive carburettor. Before you ask me for any advice, please read this disclaimer.

Disclaimer

This really isn't for the faint-hearted. After I'd collected all the info I thought we'd need, my father still estimated that it would be a full weekend's work, despite the fact that he'd already fitted the "official" Weber 32/36 DFEV conversion kit to his own camper. I couldn't see why it should take us that long. We were both wrong; it took us two and a half days.

Read this document, read around, know what you think you're going to have to do before you start and be prepared to adlib. If you break your camper, it's your camper.

The Preamble

After a lot of casting around and talking to various people about suitable carburettor replacements, a friend suggested that the Weber 32/36 DFV series carb, as commonly fitted to VW Type IV motors, was also used on the 2l Ford Cortina engine, the Pinto engine so popular amongst kit-car fiends. This seemed like a dream come true, with the DFV popular amongst some VW owners, my father one of them.

A few searches and a couple of emails to Weber later, I found that the carb used on the Pinto engine was the 32/36 DGV, a different model. Weber weren't forthcoming with any more information, but it transpired that there was only one major difference between the two carbs: one is a mirror image of the other. In most other respects they're identical. Conveniently, the footprint of the carb is such that it would be trivial to rotate it through 180 degress and mount it "backwards" on the manifold. Meaning that a DGV series carb was as good as interchangeable with the DFV, bar the location and operation of the throttle linkage. The other obvious difference was the operation of the choke. The VW, being air-cooled, used an electric choke. The Pinto, being water cooled, used a water operated choke. Hence DFEV, (electric,) and DGAV, (aqua,) respectively.

Armed with this information I phoned round local scrapyards and found a Ford Sierra with a 2l engine, and bought the carb, manifold and various hoses for £25.

I had intended building my own manifold, using the central section from the Sierra manifold to seat the carb and brazing the necessary pipework from there to the cylinder inlets. But the gods smiled and an off-chance phonecall to VWS in Manchester saw me buying a second-hand Scat manifold, designed to mount a DFV, and an electric choke conversion kit for £60.

After stripping and cleaning the carb we test ran it on my Dad's 2l camper, which fortunately has a pukka DFEV conversion on it. The carb performed well and we decided to go ahead with the conversion.

At this point we noticed a few oddities, like the vac-operated accelerator pump in addition to the mechanical accelerator pump found on the DFV, and the tendency of the pump to spew far more fuel than the DFV on my Dad's camper. It seemed to make little difference whether the vac-operated pump was conected to the vacuum or left open to atmosphere, so we left it disconnected. The mech pump continues to spew fuel liberally into both chokes when the accelerator is operated, and I fear that I'd need to start reshaping parts of the pump linkage to adjust it.

How To

This isn't exactly how we did it, but if I were going to do it again, this is probably what I'd do. From experience, it pays to make sure your plugs, HT leads and points are in good condition, your tappets are set and your timing is bang on. A fair proportion of the time spent on this project was chasing up dead ends like badly adjusted tappets and weak sparks.

I didn't have the presence of mind to take photos while we were working. The photos on this page were taken as I reconstructed the carb setup after replacing the 3/4 cylinder head. I used a cheap disposable camera, and a number of vital photos are blurred. At some point I'll take better pics with a decent camera, but I'm afraid I'm not going to strip this lot down again just for a couple of photos!

Remove existing carbs

This speaks for itself, and should be straight forward. You need to pull the carbs, linkages, manifolds, air hoses, air boxes and the hot air blower. Save all the good hoses and fittings, put your hot/cold air box and airhoses to one side for cleaning and reuse. The more space the better. Remember to plug the inlets with a rag when you remove the manifolds. Better plug the hot air feed to the air box as well. Now is a good time to pull the plugs and check them out.

Fuel and vacuum plumbing

Just inside the firewall, your fuel line has a T junction in it, to feed your dual carbs. Replace the T with a straight through, or a fuel filter, and extend the fuel line from there by, say, 18 inches. I used an armoured fuel line that was already fitted to the old carbs.

Plug up the right-hand end of the steel balance pipe that runs along the firewall, we used leftover hose with a siliconed bolt screwed into the end. A steel T-piece spigot salvaged from the original Sierra manifold offered a 5mm and 10mm connection and screwed into the cast part of the new manifold perfectly. The left-hand end of the balance pipe was connected to this tapping with 10mm hose. The 5mm vac outlet from the spigot was used later to connect the hot/cold air box.

Fit manifold

Remember to pull the rags from the inlets and fit the inlet gaskets...

Start with the left hand section of the manifold, cylinders 3 and 4. If you're working on an automatic, as we were, you're going to need to bend the ATF dipstick. With two people, one of you can get gentle heat into the pipe a few inches back from the firewall while the other exerts a gentle pull from the top, through the engine access hatch. Don't try for it all at once, better keep checking whether you can slip the manifold in, and more importantly, whether or not you can still get the dipstick in. Next, fit the right side of the manifold, cylinders 1 and 2. No problems here. Make sure everything's nipped up nice and tight.

There should be a case bolt directly underneath where you're about to place the final section of the manifold. There's a Y-shaped bracket that bolts on here to support the carb, fit it now. If, like us, you're going to have to make your own, wait until you've got the manifold together and measure up then. Offer up the cast bit of the manifold, with the tapping for the vacuum facing the front of the vehicle. We needed to grind down the casting at the exits to cylinders 1 and 4 to get the centre section to fit. Even then, the exit from the cast part and the pipe to cylinder 2 didn't line up. Again, gentle heat and judicious bending. It's easier with two people. Once you're confident it'll all fit slip the small jubilee clips down the legs of the manifolds, followed by the rubber boots. Slip the large jubilee clips onto the legs of the cast centre section and drop it in to place. Pull the rubber boots back up so that everything's sealed nicely. Fasten up the Y-shaped bracket. Tighten up all the jubilee clips. You're done.

Fit the carb

Mount the carb with the throttle linkage facing left. I had to pull the studs from the Sierra manifold and fit them to the new manifold first. These studs were designed to mount the carb on top of a heat-resistant gasket about 3/8" thick, which I also pulled from the Sierra manifold and fitted.

My Dad revived a trick he had used on engine in the past to improve fuel economy, and we fitted a wire gauze between the manifold and the heat-resistant gasket. The theory is that any large droplets of fuel will be atomized by the gauze, improving the combustibility of the mixture. Fuel condensation is known to be a problem with these manifolds, both because of the length of the manifold and the fact that it's not heated except by soak up from the heads.

Attach the fuel line (right hand side of the carb, near the top,) and the vac advance, (spigot near the base of the carb, facing the rear of the vehicle.)

Modify throttle linkage

This is where you get to play Heath-Robinson. The throttle linkage was manufactured by my Dad, with the odd idea thrown in here and there by me. We reused parts of the old Ford throttle linkage, and threw in a couple of steel plates, tacked on and shaped, to allow us to jubilee clip the mechanism to the manifold. The nice man at VWS had kindly thrown in the throttle linkage kit for a DFV, which we used to connect the throttle cable to the spindle from the old Ford kit.

As you can see from the photos there's a small steel lever bolted on to the disc and the cable is attached to the lever. Adjusting the cable leverage here allows us to vary the amount of pedal travel required to open the throttles. As it happens, with our setup the shortest lever provides us with range from fully closed to primary and secondary full open over the full travel of the pedal. Again, two people are needed here, one to operate the pedal and one to observe the carb butterflies and adjust cable tension.

Modify airbox

Even in the temperate climes of Yorkshire, my Dad's DFEV carb proved impossible to tune such that it would start cold and run sensibly after the engine had warmed up. This is because the DFEV kit he bought discarded the existing airbox in favour of a pretty chrome filter. This is a bad idea. Those guys at Volkswagen put the hot/cold air system in there for a reason, and that reason was to regulate the temperature of the air being inducted into the carburettor. This greatly reduces fuel condensation and carb icing.

You're welcome to try it without. If you live in warmer climes, you may not need to bother. If you live anywhere as cold or colder than the UK, you might suffer. In the height of summer, on an engine that's been running for hours, those manifold pipes are a lot cooler that the rest of the engine.

Strip the existing hot/cold air plumbing down to just the filter box itself, with the attached hot-air valve. You'll have to saw off the old exit pipework on the left-hand side of the box, and then plug up the hole. We used sheet cut from a handy plastic tub, and sealed the whole lot together with gaffer tape, because we're professionals.

It's a tight squeeze, but if you place chrome filter on top of the carb and balance the airbox on top of the shiny filter, you'll see that with some carefully placed holes you could mount the filter inside the old box with the hot-air input of the hot/cold air valve directly over the hot air feed from the engine. Mark up the bottom of the box, pick your point and start cutting. Carefully.

In a way this is left as an exercise for the reader. When you've finished, you should be able to mount the airbox directly onto the top of the carb and mount the entire chrome filter inside the box. Like so:

Locate the thermostat switch in the remnants on the old air plumbing -- it should be clipped into the bottom of the pipework you've just sawn off the side of the filter box. It's lozenge-shaped, a little over an inch long, with two 5mm vac pipes attached to it. This needs to be mounted somewhere in the side of the filter box. We found, in my Dad's expirements with his own setup and then when we built mine, that it's best not to place to thermostat directly in the flow of air entering the box. Doing so seems to make the system too sensitive to changes in air temperature -- you could actually see my Dad's air valve "hunting" and hear the engine follow.

You can see from the photos that the thermostat is mounted a couple of inches away from the hole where the air enters the box. Pick your spot, cut your hole, fit the thermostat. One side of the thermostat should be connected to the hot air valve, the other to the vac supply from the manifold.

With the filter in place, tap a hole through the rear of the box and thread the petrol tank breather pipe through. Tap a suitable hole through the top of the filter and insert the breather. Don't insert the pipe directly over the carb in case it interferes with the moving parts of the choke. We've grommeted the hole, to keep a grip on the pipe, to prevent chaffing and to get a decent seal.

Connect the hot-air input to the hot/cold air valve to the hot air output from the engine, directly below.

To complete the airbox setup, you'll need to make a lid. Again, an exercise for the reader.

Rejet and tune carb

Lessons in carb jetting and tuning are beyond the scope of this document, and frankly beyond the skill of the author. If you want to know more, check out the links at the end. If you're still not confident, then either find a knowledgeable friend to help you, (Dads are good for something after all,) or don't attempt the conversion.

The final setup on my 1.7l was different to that on my Dad's 2l. You'd expect that. You might also find that your setup is different again. But, for the record, here's how both carbs, are jetted:

Please note that, while the settings for the 1.7l automatic engine were taken by stripping my carb, the settings for my Dad's 2l manual, with its "sporty" cam, were deduced from notes taken at the time -- now some time ago. Also listed are settings for Robert Stockman's 1.7l engine, once resident in a 411.

The results

You should end up with something that looks like this, though your engine will be a lot cleaner, and surrounded by a less rusty bus:

I'm happy with the results. Shortly after fitting the carbs I took the fully loaded camper on holiday to Wales. We averaged 18.1 mpg. That doesn't sound so great, but let's not forget that this is a beat up old engine and an automatic transmission, and it's about 0.5 mpg better than I was getting before. Which says something for the condition of the carbs I removed.

The engine starts almost instantly, doesn't stall when warm, and ticks along quite nicely at highway speeds on the primary choke. And when hills dictate, that second choke opens up quite nicely, providing the power I need.

A word of warning, though. Be gentle with the throttle. Jamming the pedal to the metal can drown the engine, what with the gush of raw fuel from the accelerator pump and the sudden loss of vacuum over that lengthy induction manifold.

Links

The following is recommended reading:

• Carburetors 101
• How to Jet your Carburetor
• Weber Carburetor Kit -- Fitting Instructions
• Weber Carburetor Troubleshooting Guide
• Weber 32/36 DFAV Data Sheet