What size is a 24mm carb?

**Grumph** · 20th January 2016, 05:53

Originally Posted by kel

The correct answer from MNZ is exactly as per the first part of the reply i.e. "That rule does not specify whether it's at the venturi or the bore size" end of story. Besides "usual convention" doesn't fit with buckets

.

Exactly so. What MNZ and the original questioner have to realise is that what is in the rule book IS the rule. It can be varied (but the intent can't be changed) by meeting supp regs. Any clarification from MNZ is merely how someone at MNZ sees the rule - IT IS NOT A RULE.
The rule book as it stands is what we work to, not anonymous suggestions.

The only ways to define it absolutely are to either change it with a remit or protest someone and have it defined by the process of protest, appeal, judgement.
I see no reason to do either.

**Hilleye** · 20th January 2016, 21:34

Originally Posted by Grumph

Exactly so. What MNZ and the original questioner have to realise is that what is in the rule book IS the rule. It can be varied (but the intent can't be changed) by meeting supp regs. Any clarification from MNZ is merely how someone at MNZ sees the rule - IT IS NOT A RULE.
The rule book as it stands is what we work to, not anonymous suggestions.

The only ways to define it absolutely are to either change it with a remit or protest someone and have it defined by the process of protest, appeal, judgement.
I see no reason to do either.

I would definitely agree with Grumph and Kel.

I'm assuming that MNZ rules operate in a similar fashion to laws. If so, then Westminster Law principles would apply (what all NZ law is based on). That is, unless it is expressly forbidden, it is allowed. In this case if you can show somehow that a carb meets the 24mm restriction through any interpretation of the rule (i.e. somewhere in the carb body measures no more than 24mm in this case) then it is legal. This would be especially easy if it is how one or more carb manufacturers determine the size of their carbs already, which would therefore constitute a standard convention within industry. i.e. you're following industry standard practice when measuring carb size, not making up your own. Bored out carbs with a venturi, might be on the fringes, but still they're not expressly forbidden, therefore they're legal, especially if they started out as a standard 24mm carb.

The only time this would change is by precedent, which would be when MNZ actually makes a formal ruling regarding a specific location that the measurement has to be taken from or how long the 24mm restriction within a carb needs to be. In the MNZ case this would probably take the form of a supplementary regulation regarding the 24mm carb restriction. In this case it seems like all that's been given is the opinion of an MNZ official, which I wouldn't think constitutes a ruling and hence wouldn't constitute a precedent/supplementary regulation on which to base future determinations of carb legality on.

Therefore, going forward I'd say nothing has changed. If it's not explicitly stated in the rules as being illegal, it's legal. And, the MNZ opinion on the 24mm carb restriction counts for almost nothing until it becomes a supplementary regulation.

**TZ350** · 20th January 2016, 22:35

Originally Posted by Hilleye

Bored out carbs with a venturi, might be on the fringes, but still they're not expressly forbidden, therefore they're legal.

Yes, agreed, and they should be legal too. Buckets has always been about making the best of what you have, or can beg, borrow or steal, it would be a pity to see restrictions introduced with the purpose of limiting innovation.

Originally Posted by Hilleye

... unless it is expressly forbidden, it is allowed. In this case if you can show somehow that a carb meets the 24mm restriction through any interpretation of the rule i.e. somewhere in the carb body measures no more than 24mm ... then it is legal.

Makes sense. You should be able to do anything you like to a carb so long as it has a 24mm equivalent hole in it some place that all the wind passes through.

**jasonu** · 21st January 2016, 03:18

Originally Posted by TZ350

. You should be able to do anything you like to a carb so long as it has a 24mm equivalent hole in it some place that all the wind passes through.

That was part of the original intent of the rule.

**Grumph** · 21st January 2016, 06:06

Originally Posted by Hilleye

I would definitely agree with Grumph and Kel.

I'm assuming that MNZ rules operate in a similar fashion to laws. If so, then Westminster Law principles would apply (what all NZ law is based on). That is, unless it is expressly forbidden, it is allowed.

The only time this would change is by precedent, which would be when MNZ actually makes a formal ruling regarding a specific location that the measurement has to be taken from or how long the 24mm restriction within a carb needs to be. In the MNZ case this would probably take the form of a supplementary regulation regarding the 24mm carb restriction. In this case it seems like all that's been given is the opinion of an MNZ official, which I wouldn't think constitutes a ruling and hence wouldn't constitute a precedent/supplementary regulation on which to base future determinations of carb legality on.

Therefore, going forward I'd say nothing has changed. If it's not explicitly stated in the rules as being illegal, it's legal. And, the MNZ opinion on the 24mm carb restriction counts for almost nothing until it becomes a supplementary regulation.

Similar to westminister law, yes. But in no case except a protest committee can MNZ actually make a formal ruling on a machine spec question once the rule is in the book. The executive can I believe introduce an interim rule to cover any major point which arises - but that is subject to scrutiny at the next AGM.A couple of seasons back the 250 prod mess arose because as i understand it, they (or individuals inside MNZ) tried to make a set of ad hoc regs over ride the book. Couldn't be done and as expected ( by me anyway)the protest committees upheld the regs in the book. Supplementary regs usually apply only to one meeting - or very rarely to a defined series. By definition they are extras put there for a specific reason eg a local class for a street race. They have a defined life too and must be reapplied for if they are to be used again.
Be thankful we're not subject to the same regime as kartsport - there's a specific instruction "if it's not mentioned as allowed, it's forbidden"

**F5 Dave** · 21st January 2016, 17:19

Ahh, - `Wife` rules.

**TZ350** · 21st January 2016, 19:03

Originally Posted by Grumph

- there's a specific instruction "if it's not mentioned as allowed, it's forbidden"

Originally Posted by F5 Dave

Ahh, - `Wife` rules.

So true ......

**TZ350** · 30th January 2016, 22:37

Originally Posted by TZ350

The common convention has been that carburetors are sized on their choke size with slide carburetors that is measured at the narrowest point in the venture, and this is just behind the slide.

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Ok for what its worth, I finally found a reputable manufacturer who specifies where their carb is measured

**jasonu** · 31st January 2016, 03:38

Originally Posted by TZ350

Ok for what its worth, I finally found a reputable manufacturer who specifies where their carb is measured

You could use one of those on your bucket...

**TZ350** · 31st January 2016, 04:28

Originally Posted by jasonu

You could use one of those on your bucket...

AMAL

I did think about it, and they are available new too:- http://amalcarb.co.uk/t-t-series/10tt9.html

**husaberg** · 31st January 2016, 09:29

Originally Posted by jasonu

You could use one of those on your bucket...

i know its a joke but size for size a RN Amal will actually flow more air than the best Mikuni or Keihin smoothbore.
As they don't have a pesky needle hanging in the middle of the throat to interupt the flow.

The TT was a better carb on two strokes as the GP2 doesn't have a proper pilot cuircuit.
With the remote float they can also operate at any level of downdraft.
I don't think Rob needs any prompting to use some more pom bits remember he used to use a morris carb on the spliter intake

Then a holden one on his ex atac.

**Grumph** · 31st January 2016, 09:59

I wouldn't count too much on every type of Amal advertised being available. The mob making them are developing a reputation. It would appear that while starting with a hiss and a roar, they're running out of money and production is spasmodic....
Talk to the people with Concentric orders backed up for months and no delivery in sight.