How do double carburetors work


Really true...

Yes, that's right - it's actually been less than 2 months and I'm writing something. I kind of promised.

But well, this time there is also something to report from the first experiences with the new double carburetor system. Well ... and a little bit of optimization has also been done. But just look or read yourself ...

Let's start with the initial situation.


After the conversion to the IT system, it was of course first necessary to find out the driving behavior. As always, there was only rain after picking up - it was clear. So we waited longingly for the first dry days and then started straight away.

The driving behavior has changed significantly compared to the single carburetor, most recently the "39er" (converted Solex 34 PICT-3). As I had already indicated, he now turns up "more willing", looks "liberated" and grabs robustly. The 39er was really not bad - above all, I really didn't have any problems with it, but the 40s Weber IDF are a completely different league. The beetle's character has changed again. The potential of what was already slumbering in my Beetle was only really awakened now.

This is certainly also due to the fact that a lot of the rebuilding and in recent years has been subconscious was already laid out for this day. From the brakes to the chassis, transmission, ignition and the seats - the double carburetor system was now the famous cherry on the cake ... at least for me.

It's actually even more fun because you only see my Beetle's "sportiness" at second glance.

But how it is ... a "little" thing I didn't quite like optically. There were also other small optimizations.

Let's continue with the fuel line. Then I got the hint (again many thanks to Vari-Mann) that, according to the Weber manual, the same should not be higher than the float chamber of the carburetor. Vari-Mann's explanations on this were also quite easy to understand - after all, with a hanging or defective float needle valve there is a risk of the tank being drawn into the gas (overflowing). In the worst case, it will fill the cylinders with fuel while standing. That ends at the start ... rather not so good ...

I also noticed that the T-piece for the "split" of the fuel line is made of plastic - I don't really like that near hot components either.

Therefore, first of all, the cable that passed the ignition coil at the top was laid down.

02-engine fuel line

With the existing clamp (previously mounted on the ignition coil), lay the line in such a way that it does not rub on the throttle linkage or get caught anywhere else.

03 engine fuel line

Then the line "between" the carburettors is laid from top to bottom and locked in place with a cable tie.

04 engine fuel line

Oh yes ... the plastic T-piece was of course also blown out and replaced by a metal T-piece. Matching hose clamps were also included.

05 engine fuel line

Those were rather small things. Then there was the chrome air filter thing. Well, I'm not really a chrome fan - it's just kind of not mine. All right ... a few things are okay, but I just didn't want to like that with the filters. Here and there I had often seen black filter plates and of course real K&N inserts. So I probed the usual portals - but ... I almost fell off my stool at the prices that were called up.

I really had to take a look twice before I realized that they were really asking for 150 euros and more "per item" - I had always taken that to be the pair price.

Again, a tip (thanks again to Ludibug) from the forum was worth "gold". So I got in touch with Ole Braun, who has such filter flaps in various colors and variants as well as a lot more in the program. The phone call with him was also really great, really a really nice contact. So it happened that a "pair" of black aluminum plates and two original K&N filters made their way to me. (Let me give you away - there might be more to come. I'm sure to read and see another article here soon.)

06-air filter

Workmanship, feel and optics are really great - things like that are really fun! You also notice again and again when the people behind the products are passionate about it.

Of course, the plates and the filters had to move into the Beetle as soon as possible. For comparison, a picture with the chrome filter on the right.

07-air filter conversion

As it always is, one thing follows another. With the chrome filters, the housing ventilation was placed on the left of the filter. On the one hand, it was solved quite well - on the other hand, not really nice and ... the Beetle may ventilate outside with its EZ before 04/73. In this way, the gases from the crankcase do not "disturb" the mixture preparation in the right-hand carburetor.

So a new crankcase ventilation had to be found. Now, visually, I don't like the classic boxes that are available on the market. But there are other, more unobtrusive solutions in the form of so-called "tubes".


This ultimately comes from VintageSpeed, but is produced to order. It differs in some details and the price (significantly cheaper) from the version sold directly by VS.

The tube is screwed onto the "rain gutter" behind the hinges of the bonnet. It has two side connections which, depending on the EZ, vent either into the open air via a small filter or into the air filter of the carburettor. In addition, two connections for the valve cover and one for the oil filler - this is where the original connection is located on the series engine. In my case, however, the left connection for the valve cover is "dead" and only has a connection directly in the cylinder head on the right. (See below for a picture of the installed state.)

Then there were new spark plugs on the advice of the workshop - Bosch WR 78. The background was the better performance when the plugs soot in idle. Before that, NGK B6ES were in there.

09-spark plugs

In fact, the running behavior has improved a bit - or is it just my imagination? Sometimes it does.

Now we come to the (preliminary) end result of the optimizations.


So I like it very much - and before anyone asks: Yes ... the hood is now back on.

That was it for the time being - the bottom line so far: expensive fun but ultimately the right decision. And don't worry ... the next article won't take 2 years either.