Carbs are back!

**nzspokes** · 17th March 2016, 21:03

I want a pair of these

http://www.bikebros.co.jp/vb/sports/...carburetor-en/

**AllanB** · 17th March 2016, 21:16

I was immediately going to say - fucking carbs EFI rules.

But

They are quite beautiful.

They should be exposed within the frame for all to see.

I want one just to mount on the wall as a work of art. Mrs B may not agree.

**kiwi-on-wheels** · 17th March 2016, 22:48

Dear god those yoshi carbs are beautiful

**Autech** · 17th March 2016, 23:55

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**neels** · 18th March 2016, 09:41

They do look pretty, although I'd hardly call it a revelation, Mr Weber figured out some decades ago that it was a good idea to have the fuel delivered to the centre of the venturi.....

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**Bass** · 18th March 2016, 09:54

Originally Posted by neels

They do look pretty, although I'd hardly call it a revelation, Mr Weber figured out some decades ago that it was a good idea to have the fuel delivered to the centre of the venturi.....

Yeah but it's not the same in an important aspect though.
The Weber has a throttle butterfly while the fuel addition point is fixed geometry. That means the airspeed past the fueling point varies hugely with throttle opening.

The Yoshi is a slide arrangement that opens and closes fuel ports with the slide. That means the airspeed past the fueling points is much more constant and typically higher than the Weber, thus giving much better atomisation across the whole operating range

**neels** · 18th March 2016, 10:10

Originally Posted by Bass

Yeah but it's not the same in an important aspect though.
The Weber has a throttle butterfly while the fuel addition point is fixed geometry. That means the airspeed past the fueling point varies hugely with throttle opening.

The Yoshi is a slide arrangement that opens and closes fuel ports with the slide. That means the airspeed past the fueling points is much more constant and typically higher than the Weber, thus giving much better atomisation across the whole operating range

Yep, that's the difference between a fixed venturi and cv carb.

The change is where the fuel is supplied in the variable venturi which makes sense. So the obvious question is why didn't someone think of it sooner, or is it just a case of the cost/benefit didn't stack up, or is it not worth the effort as EFI is still going to be better.

**Bass** · 18th March 2016, 12:58

Originally Posted by neels

Yep, that's the difference between a fixed venturi and cv carb.

The change is where the fuel is supplied in the variable venturi which makes sense. So the obvious question is why didn't someone think of it sooner, or is it just a case of the cost/benefit didn't stack up, or is it not worth the effort as EFI is still going to be better.

Good questions and I'm no expert. However, it seems to me that this is the first carby that I have seen which makes a real effort to atomise the fuel. All the others that I have had in bits over the years, really just poured the fuel into the airstream and relied on downstream turbulence to achieve mixing. It seems that the turbulence around the inlet valve is high enough to do a pretty good job here. Note that Yoshi claim improvements in fuel economy for this device, which is to be expected and especially at part throttle settings, but they are not screaming it from the roof tops. So it's fair to assume then that the improvements are worthwhile but not revolutionary. Will need very careful fuel filtration but.

I repeat that I am no expert, but from the little that I know of modern, common rail fuel injection systems, they are just so versatile and way more accurate than a carby can ever be. I don't know how many fuel impulses per cycle are usably possible, but I have heard up to 7 in use on some diesels. They are way more complex of course and so harder to fix on the roadside.

**nzspokes** · 18th March 2016, 13:03

Originally Posted by AllanB

I was immediately going to say - fucking carbs EFI rules.

But

They are quite beautiful.

They should be exposed within the frame for all to see.

I want one just to mount on the wall as a work of art. Mrs B may not agree.

The big deal is it sounds like the needles will be available as a part.

**Motu** · 18th March 2016, 16:58

[QUOTE=Bass;1130956443 just poured the fuel into the airstream and relied on downstream turbulence to achieve mixing.[/QUOTE]

The emulsion jet mixes air with the fuel...in the carb. That's those top jets on the Weber, and on a motorcycle carb, an airbleed from the horn into the needle jet. So, emulsified in the carb body, atomised as it enters the airstream and vaporised with heat and vacuum. Needle jet carbs are very dirty, that's why the SU was dropped suddenly for cars, put them on a gas analyser and they were very high CO and HC. Motorcycle carbs the same, it's just that they never had to pass the same emission tests as cars. There is always room for improvement....so long as it doesn't hurt power.

**Ocean1** · 18th March 2016, 18:27

Originally Posted by Bass

However, it seems to me that this is the first carby that I have seen which makes a real effort to atomise the fuel.

Atomisation particle size doesn't automatically correlate to higher eficiency combustion.

In't dark ages you might run a DCOE Weber for good power at max rpm for track work, but the near identical Delorto for better response through mid-range for hillclimbs. The very slight differences caused slightly finer lumps in the Weber.

Edit: That's a fucking nice idea with the multi-port hollow needle though. I've made flow meters like that before that have used the same advantages in a better spread of sample points, it obviously works just as well in reverse.