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Something different: 1975 RD125 2 stroke carb

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Well,

This is a little out of the ordinary for TT but I figured there's a lot of knowledge here so I'll give it a try.

I just purchased a 1975 Yamaha RD125 two-stroke street bike. I'm cleaning it up and cafe' racering it.

The issue is the carbs. It's a parallel twin so it has two 18mm TeiKei carbs. There is absolutely zero support for these and I cannot get larger jets or anything for them.

I'm thinking of fabricating a two-into-one intake plenum and running a single, larger carburetor such as a 36mm off a YZ125 that I can actually get parts for.

Anyone have any thoughts on why this wouldn't work? Can I just add the two smaller carb bores together and spec a carb that has that plenum size?

It would make it so much easier to jet and run throttle cables for a single carb

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yeah, those kits are all over ebay.

Issue is that I need more jet options other then the stock size. I deleted the oil injection and I'm running premix and pod filters so I need to go up a couple sizes on the main.

you cannot find larger main sizes

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yeah, those kits are all over ebay.

Issue is that I need more jet options other then the stock size. I deleted the oil injection and I'm running premix and pod filters so I need to go up a couple sizes on the main.

you cannot find larger main sizes

So, drill out a main jet that you already have.

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I've thought about that

But drilling jets is really inaccurate and the chances of my be able to drill two of them to the exact same size (two carbs) is slim

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Why did you drop the oil injection? Properly setup, it blows away premix. And it would solve your jetting dilemma.

Drilling is a very hit or miss deal, with the difference in flow between one size and the next, especially on a tiny engine (62.5cc a cyl). You'd need a lot of jets to finally get lucky as even a slight miscue with the drill will have a big effect. Jets from the manufacture are not drilled, they are reamed to ensure even sizing. Then they are measured and marked with the size.

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I'm ditching the injection because I'm cleaning up the rear frame and getting rid of the oil tank.

I would have to rejet even if I didn't get rid of the oil injection since I'm running pod filters

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Gotchya. Just wanted to make sure there was a reasonable explanation instead of "Because a guy I know said to..."

You could source a pair of Mikuni round slide carbs (2mm larger or so) and then have no jetting issues. The Teikei's, they must of been real cheap for Yamaha as not one carries any jets. Bad move for an OEM to use them.

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