What size is a 24mm carb?

[Yow Ling]

I can't believe this is not clearly defined in the rules - mind you no being so clear leave it open to modifying as above which is also good for development.

Me - I agree - provided there is a point within the carbs physical inlet makeup that measures 24 mm it's 'legal'.

thats wide enough to drive a bus through, the measurment should be square mm, which is what the "equivelent" alludes to equivelent of 24mm carburettor is 452mm2, I like the idea of it bieng measured within the carb body.

Actually a definition of a carb is also important, in this age of efi

[Grumph]

thats wide enough to drive a bus through, the measurment should be square mm, which is what the "equivelent" alludes to equivelent of 24mm carburettor is 452mm2, I like the idea of it bieng measured within the carb body.

Actually a definition of a carb is also important, in this age of efi

That last is true and relevant. I also like the idea of quoting it in mm2.
my earlier idea of passing the intake air through a 24mm hole, while easy to police, is open to the use of heimholz resonators attatched to big carbs...
Don't know if that's a good idea or not.

[richban]

That last is true and relevant. I also like the idea of quoting it in mm2.
my earlier idea of passing the intake air through a 24mm hole, while easy to police, is open to the use of heimholz resonators attatched to big carbs...
Don't know if that's a good idea or not.

The pass through a 24mm hole is so easy to police. Why make it hard? Really what is a good reason to make it anymore difficult than that?

[Yow Ling]

The pass through a 24mm hole is so easy to police. Why make it hard? Really what is a good reason to make it anymore difficult than that?

It depends where the hole is, if it just feeds the airbox it is the same as 2 x 24mm carb equivelent, also some carbs are not round , like nsr carbs

[Grumph]

The pass through a 24mm hole is so easy to police. Why make it hard? Really what is a good reason to make it anymore difficult than that?

Slow down - i'd simply suggested that all intake air had to pass through a 24mm hole - i didn't specify it had to be part of the carb(s)
This could conceivably mean a big airbox with forward facing entry using a venturi with a 24mm bore...which may not be the best way to restrict a 125....

i'm still in favour of wording it so that at some point in the carb body the passage may not be bigger than 452mm2 (assuming mike's maths are correct)
i see no point in specifying that this has to be for so long a distance. You may well be ruling out a usable carb by doing this, some pumpers have a very short venturi.

[richban]

Man I get bored easy these days.... Carb rules are dum. Lets just build open 50cc F5 bikes.

[TZ350]

30mm vis 24 in a back to back test. Red line = 24mm carb Blue line = 30mm carb, not much difference.

So 24 or 30 the power was pretty much the same.

So what are we really trying to achieve with a 24mm carb restriction for 2T's that are over 104cc. Remember this carb restriction also applies to those 100cc builders that have taken the easy no de stroke option and are using the oversize (107cc MB100) KT100 pistons.

All this restriction talk is about carbs, EFI is not mentioned in the rules, so does that mean throttle bodies are open? ...

If we have to have a restriction then I favor the "all inducted air has to pass through a 452mm2 orifice at some point" approach.

That gives you a restriction but leaves the door open to unrestricted innovation which is one of the attractive features of Bucket Racing.

[richban]

So what are we really trying to achieve with a 24mm carb restriction for 2T's that are over 104cc.

I think its to give the 4 strokes a small chance at keeping up.

[speedpro]

It's funny, originally the idea was to restrict the 125cc engines to the carb that they were mostly fitted with by the manufacturer, that being a 24mm carb. I worded it that way to stop clever buggars using more than one. Things have moved on of course. Nobody considered fitting a suitably sized venturi to a larger carb, until Rob came along. I still think it's more or less worded OK and also that the 24mm has to be part of the carb, not somewhere else on the intake system.

I think the rules are clear that you can use any size fuel injection throttle body you like. After all it does not mention them anywhere in the rules. Technically you also have to run a 24mm carb, because it does say that in the rules. It doesn't say "if you have a carb" it must be a certain size. It says bikes running a certain engine are restricted to carburation equivalent to a single 24mm carb. There's a restriction there.

[TZ350]

So what are we really trying to achieve with a 24mm carb restriction for 2T's that are over 104cc.

I think its to give the 4 strokes a small chance at keeping up.

............. true, but I am still waiting to hear of a 2T winning the BOB.

[TZ350]

I think the rules are clear that you can use any size fuel injection throttle body you like. After all it does not mention them anywhere in the rules. Technically you also have to run a 24mm carb, because it does say that in the rules.

Hmmmm now EFI is a reality, does this mandatory 24mm carb actually have to work?



At 30 rwhp Speedpros unrestricted 100 Blue line betters my 125 in the dyno stakes. It is something anyone could do if they applied themselves like Speedpro has.

Things have moved on, EFI is a reality. So what do we really want to achieve here. And do we still need an induction restriction at all? Or should all 2T's be restricted to 24mm's? probably.

[cotswold]

Man I get bored easy these days.... Carb rules are dum. Lets just build open 50cc F5 bikes.

Richban for president 😎

[jasonu]

I think its to give the 4 strokes a small chance at keeping up.

Nope. It was to offset the 25cc advantage they had over the current for the day 100cc watercooled motors.

[FastFred]

Nope. It was to offset the 25cc advantage they had over the current for the day 100cc watercooled motors.

Now that 100's are allowed to go out to 110cc on re bore, is the restriction still relevant.

A 100cc water cooled motor already has an enormous advantage over air cooled engines, maybe to be fair, the water coolers should be restricted to 24mm and the air cooled engines unrestricted. Now that would be more balanced.

[richban]

110cc on re bore, is the restriction still relevant..

Re bore is short for – replace bore – right