Well get ya thinking caps on fellas .............

[mcbob]

I'm in the process of upgrading the humble SP125c to run in our stock appearing saw races and have fitted a Mac sloper manifold to the engine by just cutting a small section out of the old fuel tank now it's all in there but here's the question what smaller outside dimensioned carb can i use to replace the BDC carbs i have, plus the old style (HL) won't fit as it's too big as well in physical size maybe something in the smaller square style carby's would be the way to go.

Anyway have a squint at what i have been up to on a wet and misable day downunder.

http://macbobaust.com/sp125_v4.html

Mc Bob.

[Rob Voska]

How about a 100cc Yamaha Carb? It's small and should fit in the space you have.

[mcbob]

How about a 100cc Yamaha Carb? It's small and should fit in the space you have.

Got any more info or spec's on these Rob ?

Mc Bob

[Rob Voska]

W3BA is 1 1/2" thick and 2 3/4" x 3". You should be able to find one at a kart track easy.

[Mark Brubaker]

Those Walbro's use an external pulse line Rob. Would that be a problem McBob?

Mark

[Gordon Duax]

McBob,

Somewhere here in my piles I have an adaptor to put the WB3A on a Mac manifold......
And there is a larger bore version of the WB3A......(WBxx...).
The one I used had a 1.125 throttle plate, and about a 1.062 venturi if I rember correctly.
Was just something I played with.
If I find it, i'll send you some pictures.

By the way, the WB series has the same bolt pattern as an HL.

[Gordon Duax]

Bob,

This link has all the WB series listed, and when you click on one of the numbers, it shows thre venturi size.

http://wem.walbro.com/walbro/group2.asp?FamilyName=WB

[mcbob]

[quote="Mark Brubaker"]Those Walbro's use an external pulse line Rob. Would that be a problem McBob?

The Sp 125 had a pulse line coming off the outside of the reed plate then by rubber line to the carb but it wouldn't be hard to fit a pulse line to the sloper manifold.

Mc Bob.

[mcbob]

Thanks Gordon i see that the odd one goes to 28mm .... i know this is a silly question but is that the largest venturi size available in these carbs or types of carby's.
Especially since Mac ran a 35mm in the BDC.

Mc Bob.

[Gordon Duax]

As far as I know Bob.
The limiting factor is the space between the mounting bolts, and possibly internal dimensions.
The big one I have was bored that big from a standard Yamaha WB3A.
So possibly, the one that comes 28mm could be streched a little bit more.

But personally, I think the BDC is just too much flow path for what reeds it has to go through anyway........

On my 125 oval track bikes I run years ago, I never went above 28mm.
There were a lot of people trying larger carb (bigger is better, right?)
But I always out powered them....