Carburettors eligible for pre-65 Trials

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David Lahey
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Carburettors eligible for pre-65 Trials

Postby David Lahey » Sun Jan 21, 2007 10:52 pm

I'm thinking of proposing a change for the MA Manual of Motorcycle Sport which would allow the use of any round slide carburettor for pre-65 Trials competition.

Does anyone have an opinion on this one way or the other that may help me write the proposal?

Thanks
David



Mark K
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Postby Mark K » Mon Jan 22, 2007 8:57 pm

David,

First let me start off by saying I don’t have the experience or expertise to have an opinion on this, but I do have a question.

MOMS only seems to mention this in 23.5.0.2 23.5.0.3 and 23.5.0.4 . The way I read this you are not necessarily restricted to original equipment for any particular machine, but must fit a carby that was made pre 1965, or you can use something newer that is visually indistinguishable from a pre 1965 one. Apparently there is nothing to stop you internally modifying such a carby any way you want or need.

I’ve just realised I have 2 questions

1) Why would the current situation be a problem?
2) What would anyone actually gain under your proposal?

I’m not trying to knock the idea, but I would imagine you would need to clearly address both those questions in any such proposal. And since I don’t understand the problem I thought it couldn’t hurt to ask.

Mark.



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Postby David Lahey » Mon Jan 22, 2007 10:49 pm

Thanks Mark
I'll have a go at explaining.

There are a few reasons for why we should be able to use any round slide carby on a Classic Trials bike.

1. The most important reason - to make it easy for the scrutineering people who decide if a bike is eligible to compete in the class.
While anyone can tell a Mark 1 concentric AMAL from a Mark 2 concentric AMAL, very few people are experts in knowing when a particular Mikuni or Keihin two stroke carby became available. How would someone prove that the carby on their Classic trials bike really was from a 1963 Yamaha road bike and not from a 1967 Yamaha road bike? They probably selected it from a box of carbies at a bike wrecker and have no hope of even knowing for themselves exactly when it was made let alone proving it to a scrutineer. The documentation just isn't available to help decide.

2. A modern Japanese round slide carby has no technological advantage over a Japanese round slide carby made in 1964, but it is much easier to find a newish carby in good condition. If someone is contemplating building a Classic Trials bike, finding a very old carby in good condition should not be used as a hurdle to entering the class. Of course it is possible to buy a brand new AMAL Mark 1 carby at great expense and stay within the rules but why not allow someone to buy whatever round slide carby they can from a wrecker and join the Classic class within a reasonable budget?

3. Australian Pre 65 Class rules for MX already allows the use of any round slide carby.



Mark K
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Postby Mark K » Tue Jan 23, 2007 2:03 am

OK Thanks David,

That's simple, straightforward, and logical. For what its worth, it sounds perfectly reasonable to me.

How approachable are MA when it comes to this sort of thing? I wouldn't have any idea where to start. but there must be people at this site who know much more about that process than me.



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Eligible Carburettors

Postby Fraser » Fri Jan 26, 2007 9:42 am

David,

After prompting by a certain fellow who wears yellow I made a similar application to MA in 2003 and received a response on behalf of MA from Chris Leighfield who had carried out considerable research to identify carburettors manufactured prior before 1965. He encouraged me to circulate the following list amongst classic riders and forward any additional information, which could be included.

Caburettors permissible for Classic Trials Competition in Australia

The following is a list is in addition to those carburettors eligible by reason of being original equipment on engines meeting the requirements of the rules.

All carburettors must be of round slide construction and have conventional operation.

Amal – TT, Monobloc, Concentric Mk1 (the latter two are in the GCR already and TT is very old so probably not worth mentioning)

Bing – as fitted to Fichel and Sachs motors up to 1969

Dell Orto – (not yet had time to research)

IRZ – as fitted to original Bultaco Sherpa T (since words “not Spanish” were removed from the regulations a few years ago at the instigation of someone who shall be nameless)

Keihlin – as fitted to small capacity Hondas from 1962 onwards. (This model was still fitted to XL, TL etc until at least 1985 so is probably the most suitable for small four stroke engines).

Mikuni – as fitted to small capacity Suzukis from early sixties. ( This is probably the most suitable for two stroke engines. I’m not sure how long the model continued but my guess is that it would have been around for a number of years).

Villiers – S25 etc As fitted to all D, E and A series engines.

END

If you check out the pre 65 Scottish regulations you will find that they are more stringent so I suggest that you leave sleeping dogs lie.

http://www.ssdt.org/sitebody/modules/Up ... 202007.pdf

Why are you suddenly interested in pre 65 carburettors anyway?



David Lahey
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Re: Eligible Carburettors

Postby David Lahey » Fri Jan 26, 2007 1:32 pm

Fraser wrote:David,
Why are you suddenly interested in pre 65 carburettors anyway?


Very perceptive there.

There is a two stroke pre-65 trials bike on my horizon and I noticed that the MA carburettor eligibility rules were rather difficult to enforce when it came to Japanese carbies, leading to potential conflict between riders and possibly putting potential riders off from joining in the fun.

I'm not concerned for my bike as it will most likely have an AMAL Mk1.




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