I've been working on quite a few of these old Yamahas lately. Great little motorcycle and possibly under appreciated as collector bikes. The bike below is a YD2 that I went through and got running for a customer.
Terrible pictures but you get the idea. I'm finally finished enough where I can get to work on a limited basis. On the table is a Yamaha YDT1. 250cc 2-stroke engine. I guess you could call it the "sport" version of the YD3.
These pictures are already dated as the front "non-shop" area has had some additions to it. Better pics to follow.