Hi Pyo, I don't have a picture but if you look on top of the clutch housing, you should find a cover that you can remove to gain access to the pinion end. On the D2, there is both the main clutch cover and also a small round cover about 2" diameter. You may have something similar on the D6. If you have the small round cover, you can poke a screwdriver in there, push on the end of the latch lever to disengage it. I'll see if I can find a picture but someone might already have one they can post

Is it starving of fuel? I had an old batch of gas put in my 5U's pony and it ran like a bucket of bolts - had to have the choke on to get it to run enough to start the main. Will be swapping out without delay : )

Does it behave the same way if you a) turn on the fuel and let the bowl fill, then b) turn off the fuel and start it. Does it also run for 30s on just a bowl full of gas (or 10s or something). If so, there could be detritus somewhere between the fuel tank and the bowl. One of the members here had a tractor that would often conk out at random periods. It would start right up again and then run for some other random length of time. Turned out to be a foreign object in the tank that he couldn't see that would occasionally block the outlet. After changing easy things like the plugs, the wires, the condensor and points, and cleaning the fuel bowl, I'd start at the tank and positively confirm everything downstream is clean and clear. By positive I mean run flow tests, not just a "look" for an extended period of time. For example, fill the tank with fuel, and confirm that it will run through the tank, the pipes, the carb fuel bowl without degradation until the tank is empty. At some point, you have to work methodically and thoroughly to isolate the problem.