This is inspired by the pictures in the recent post by ClassicFiat500 about his backfiring hot rod. I was taken by the absolute overkill look of the Weber side draft on top of the tiny engine.


I had the following idea for my -59 Bianchina, the one that I'm hot rodding. Or maybe "warm rodding" is a better phrase? (The -58 Nuova will stay as original as possible.)

I have a small stash of vintage Weber DCOE and Dellorto carbs, and instead of 28/32 or similar I'm thinking of using only one of the barrels of a 40mm side draft carb to supply the engine, and block off the other barrel. Kind of like the split-Weber setup they used on some racing Mini Coopers. I'm thinking of using the nice Alfa "rubbers" to connect, but I would have to fabricate an elbow for the intake, brackets etc.

Has anybody tried a similar setup before, and if so, what were the results? Any big "gotchas"? More importantly, is this a really dumb idea?


Please encourage or discourage!

This idea of using just 1 choke of a 'twin' carb has been used before in anger. At one time "Formula 3" regulations allowed for a 1,000cc engine, but just 1 carb choke.The system at that time was to do just what you are suggesting--a twin choke Weber side-draught, with one choke blanked off. Cosworth got about 110BHP out of the MAE, but when Broadspeed put the same engine WITHOUT the carb restriction, they realised 130BHP out of the same 1,000cc engine!
You can get commercial manifolds for fitting both the DCOE and the Dellorto side-draught carbs, so that wouldn't be a problem. However, if you could get hold of a GOOD Dellorto FZD, that would be a better carb for what you want to do

Why not fit a Weber 30DIC , a twin choke downdraught carb that was a traditional tuning modification. Having a progressive choke arrangement you can drive on one choke with part throttle then have the twin choke experience when you give it the beans. Alternative would be the Weber 30DGF from a Panda 30. It always seems to me that the evolution of standard carbs on the little twin cylinder engines is very much overlooked. Fiat 500 - Weber 26IMB, Fiat 126 - 28IMB, Fiat 126 Bis - restricted Weber 30DGF, Fiat Panda 30 - unrestricted Weber 30DGF.

Weber 30DIC

Yes, I do like the traditional look of a twin choke downdraft very much, and it's probably the way I will go with the -58 Nuova, where a very clean, original look is the mission. Alternatively just stick with a single barrel, possibly an FZD like Tom suggested - the best looking carburetor in the world. Down the road I will bug you guys on advice for such a setup.


Now the -59 Bianchina has a different mission. It's an extreme low-budget build starting with what's essentially scrap, thus I want to use what's on hand. At the same time the mission is style, or maybe more correctly complete lack thereof. It's not meant to be a high performance car, it's meant to look outrageous and borderline bizarre, if possible in a Hot Wheels fashion. Basically look fast while in reality being quite slow. So after looking at those pictures I thought a giant side draft perched on top of a miniature engine would be the perfect accessory for a cars-and-coffee head scratcher.

Now I can almost hear you: Why? Why? Why? Because you only live once.

500nuova said:

This is inspired by the pictures in the recent post by ClassicFiat500 about his backfiring hot rod. I was taken by the absolute overkill look of the Weber side draft on top of the tiny engine.

Click to expand...

Hi 500n, I wouldn't get too taken by the size of the weber carb in your quoted post, yes it is big, but these carbs are very flexible in their fitment to various engines. The secret is not the size of the carb intake throat (40mm) it's the size of the venturi fitted Inside the throat that matters, these can be as small as some 28-29mm (don't quote me!) and therefore can handle the engines air intake requirements by providing the velocity required for good atomisation and carb performance. One of my engines uses a Solex 32PHH-10 which is smaller and lighter carb with fixed venturi of 31mm. After crunching the numbers I found that 31mm is about as big as I needed to go to for good performance given my engine tune. My other engine of lower tune uses a Weber 30DGF as mentioned in the thread, this does indeed give good performance with remarkable fuel efficiency at the same time. One of the reasons I use these carbs is the availability of parts and the common fitment to other Fiat/Italian cars.
Ian.

Thanks Ian,


I realize the importance of the air velocity and would size the venturi (sic! singular) and jets accordingly. From what you say it sounds like about 30mm venturi would be plenty for my purposes.

Taking this route for the Bianchina would be mostly for looks rather than for performance. Big carbs turn heads. So do multiple carbs. Thus another idea I'm playing with in the looks department is to use three or four very, very tiny Mikunis on a shared manifold. Thoughts on this?

Dual Mikuni (or Keihin) carbs are quite common in Italy---they often use adapted Weber inlet manifolds. BUT is is also quite common in Italy to fit 4-port heads, which therefore can utilise the benefits of a dual carb set-up. However, the 4-port heads they use in Italy are NOT Panda30 heads--they are specially cast (or modified 'normal' heads) so that the 2 inlet ports are further away from each other than on the Panda30 head. Technically, the Panda30 inlet ports are too close together, so the ports on the special heads are designed to be an almost straight flow into the inlet valve. It might look impressive at 'cars 'n coffee' meets to have a muti-carb set-up, but if you are retaining the original design 3-port head, fitting more carbs will gain you very little, if anything---only so much can go through the single inlet port.

500nuova said:

Thanks Ian,


I realize the importance of the air velocity and would size the venturi (sic! singular) and jets accordingly. From what you say it sounds like about 30mm venturi would be plenty for my purposes.

Taking this route for the Bianchina would be mostly for looks rather than for performance. Big carbs turn heads. So do multiple carbs. Thus another idea I'm playing with in the looks department is to use three or four very, very tiny Mikunis on a shared manifold. Thoughts on this?

Click to expand...

Hi 500n, yes twin Mikunis etc would do the job fine after set-up. But, it purely depends on how deep your pocket is????? It is quoted that a standard head will flow well to 6000 rpm (when prepared correctly) above that the Panda head will flow better (when prepared correctly) up to some 7500 rpm depending on preparation and valves etc above this level you need MONEY for cast heads and cranks and special internals. These engines will perform to 8000 rpm + all it takes is money!!!!!!!!!!
Ian.