Now I'm rebuilding one

[Drew]

Do the rules mention a sideways measurement? I'd have thought that if the inlet wasn't round the measurement would be taken at it's widest point.

They don't, but nor do they say anything about what shape they need to be at all. A square 24mm carb has a surface area of 576 square mm. A round one 452.4 square mm.

Now I know that no one has made a square carb for the detriment of flow it'd cause, but there are many different shapes that have been fashioned, and surface area is quite hard to be exact about?

[mossy1200]

You would be better to get a cr carb and remove the head side flush then open 2 inlet manifold holes so the carb becomes a Y intersection and take each outlet directly to each inlet.

[Yow Ling]

It doesn't say "round hole" anywhere in the rules is kinda what I'm driving at.

The rule is pretty easy to understand, carburetion equivelent of a single 24mm carb gives you 452 square mm , I guess you knew that when you figured out that 2 x 17mm carbs were within the rules, no need to cheat, carb isnt really a restriction on making lots of power

[Madness]

A square 24mm carb has a surface area of 576 square mm. A round one 452.4 square mm.

And a square 24mm across the flats measures 33.94mm at it's widest point, diagonally

[Drew]

The rule is pretty easy to understand, carburetion equivelent of a single 24mm carb gives you 452 square mm , I guess you knew that when you figured out that 2 x 17mm carbs were within the rules, no need to cheat, carb isnt really a restriction on making lots of power

17mm is gonna be pretty restrictive per 67cc I reckon, but I'll try both the flat slides sleaved down, and a single 24mm flat slide if it works at all.

[Henk]

What would be the legality of an oversize carb I.e. bigger than 24mm with a space on top of the slide to stop it opening past the relevant area? Probably wouldn't help top end but may help elsewhere.

[koba]

17mm is gonna be pretty restrictive per 67cc I reckon, but I'll try both the flat slides sleaved down, and a single 24mm flat slide if it works at all.

24mm per 62cc is pretty good though innit?

I think the square idea is queer, screw that; a single 24mm on a manifold has to be worth the effort.
Undeniably legal and huge area for a 125, 62cc for a 24mm carb.
I'd guess it might take a bit of trial and error to get the right balance between length and shape. (ie short=good straight=good)

As I'm sure I've said before; I'd give this a nudge if I wasn't already fully committed.

[koba]

What would be the legality of an oversize carb I.e. bigger than 24mm with a space on top of the slide to stop it opening past the relevant area? Probably wouldn't help top end but may help elsewhere.

Smart brains. I guess it fits the rules but surely wouldn't be as good as a purpose built 24.
Maybe good as a stopgap.

[mossy1200]

Take the head end all the way off a round slide cr leaving only the 24mm outlet hole and weld 2 curved ally pipe prejoined to meat at 24mm. Shape and weld to the cr carb body.


A flat slide would be alot harder to fashion if your after a short inlet manifold.

[speedpro]

It's been done before using copper plumbing fittings and a single 24(?)mm carb. The carb mounted on the foot of the "T" and each leg of the top of the "T" fed one cylinder through a 90deg bend. Worked a treat. If you can't solder the bits together use araldite

[bucketracer]

The rule is pretty easy to understand, carburetion equivelent of a single 24mm carb gives you 452 square mm , I guess you knew that when you figured out that 2 x 17mm carbs were within the rules, no need to cheat, carb isnt really a restriction on making lots of power

452 mm2 is what the fast boys are working with.

It's been done before using copper plumbing fittings and a single 24(?)mm carb. The carb mounted on the foot of the "T" and each leg of the top of the "T" fed one cylinder through a 90deg bend. Worked a treat. If you can't solder the bits together use araldite

A single 24 and Y junction inlet would be my pick for a 125cc 180deg twin as each cylinder is only sucking for half the time so two 62.5cc cylinders could easily share a single 24mm carb.

TeeZee has sucked 34 crank hp through his 24mm OKO carb, so the 24mm carb rule as its commonly understood is probably less of a restriction than Bucketeers used to think.

[Drew]

Some good info, especially that the single carb has been done before. If pulse timing doesn't screw it up then it would seem that 24mm single carb is less restricting for me running a twin than a 125 single.

Bonus.

[TZ350]

I think you would be on the money with a single 24mm carb on a 125 twin 2-stroke. I was planning on doing that with a GT125 twin we have here.

[Drew]

I think you would be on the money with a single 24mm carb on a 125 twin 2-stroke. I was planning on doing that with a GT125 twin we have here.

Me too. Only issue I can think of is if there's a pulse timing clash, and keeping enough gas in the bowl.

[Paul in NZ]

Mount a single card on a longer Y manifold and it should help with the torque. FWIW the new redesigned (almost up to the 80's now by golly) Moto Guzzi V7's have a single injector on a long Y manifold and its claimed it increased all the good things and decreased all the bad things....