When I first got my k7/k6 donor bike running I had a fuel leak from the drain tubes, I cleaned the float valves/checked float heights etc but still had a leak from No3 drain, it was only when I swapped float bowls 3 and 4 over and the leak followed the No3 float bowl that I looked closely enough to spot a hairline crack in the thin brass overflow tube in the float bowl, not sure if this is caused by moisture freezing in the tube or vibration but it's not as uncommon as you might think, just thought I'd mention it in case someone else gets this issue.
Top tip - always keep a small fire extinguisher within easy reach whilst working on the fuel system, and remember to put your hands out first!
