I think these are the o rings from Home Depot


www.homedepot.com/p/DANCO-36-O-Rings-10-Pack-96750/100259321

Amazing how a 25 cent rubber ring can save so much trouble

Carb has 311 E2 stamped on flange. Images attached.

I think 311 is a RT3 if I'm not mistaken

DT2 or DT3 .. I think Mark T had said the E2 was the later produced DT2... But both used the 311

It's a DT2 for certain.

Yamahahaha: Home Depot: one of my go-to places when I'm in North America. That won't be happening for a while, though.

Pete-RT1: The diagram in your image is completely different from my carb layout. But my carb layout when I pull it apart matches the workshop manual I have.

I'll see if my local carb specialist has an o-ring, after that I'm going to try one more thing - raising and lowering the needle a notch each way (it's in the middle one), and if that doesn't work then dump it with a carb specialist.

The carb on your bike looks the same as the one I posted the exploded diagram for. The 311 is also correct. As Pete asks, where are you seeing differences?

Yes, the 'O' ring is shared over different models.

Pete and Great. Sorry, I'm going mad. It's very similar, but I don't see what looks like an external pipe to the main jet banjo bolt in the diagram on mine.

Hi Iain, it's difficult to see on the diagram but the pipe heading down towards the banjo bolt for the main jet doesn't connect to anything. I can see on you photo the pipe is missing on your carb.
If you take a look on CMSL you can zoom in.
I've got to order the same o-ring for my RT1 and I think Simply Bearings have them based on yamahahaha's link with the dimensions.
Simply Bearings' sizes are metric so 1.6mm section, 4.7mm id, 7.9mm od should do it, go for Nitrile.
Here's the link to CMSL for the diagram www.cmsnl.com/yamaha-dt2-1972-1973-usa_m.../partslist/B-09.html.
Hope you get it sorted, Pete

I must be driving you guys mad. I bought a DT because it was supposed to be simple.

Anyway: what is the five-digit number for the needle jet? All I have is a jet with no numbers on (and which looks like it's been installed by a gorilla using mole grips anyway), a book that says "N-8", and a carb guy who says he needs the five digit number that's usually stamped on the jet. Where? The inside is the only bit I've not forensically examined.

Don’t disregard that pod air filter. It has been shown to cause a lot of high speed running issues with aftermarket filters. I played with several setups before conceding the stock filter sometimes is best. Just saying.