Muang Khong and Huai Ya Sai are only some 24km apart, seperated by a little stretch of 4WD dirt on David's MHS Loop map. Having a hankering to get a little dirty, I decided to set out from Chiangmai one afternoon to explore this little stretch of trail. The first leg was to get up to Chiang Dao on 107 and then turn west following signs for the Chiang Dao cave. The road to Muang Khong goes through a wildlife sactuary and it's necessary to purchase a ticket before passing through. To get the ticket, you first have to go to the headquarters of the sanctuary. You'll come to a Y intersection at(N19'24.106 E98'55.696). First, take the left fork and then look for a steep uphill road to the right that leads to the office. You'll also see a sign for the sanctuary. It cost me 200 baht to get one ticket for me and one for the bike. After that, backtrack to the Y and take the other fork. When you get to the guarded gate (N19'24.831 E98'54.890) hand over your tickets and keep going. The road from there is concrete and in very good condition. It's narrow and steep though, so be sure to keep an eye out for oncoming traffic on blind turns. The route is very nice with rugged mountains all around. There's a nice viewpoint area (apparently unofficial) on the north side of the road (sorry, no waypoint). It has a little straw shack with a view of the valley below. When you finally get to Muang Khong, there's a small restaurant where you can have a drink and watch some boxing on the TV with the local characters. One thing I've noticed is that Thai boxing fans don't differentiate between good solid hits and glancing blows in a match. They just ooh and ahh at every contact. Anyway, the dirt trail starts on the far side of town. As with many small villages, there are alternate paths that you'll have to sort through to find the one you need. I kept asking locals if I was on the road to Huai Ya Sai. If you have a GPS unit, head to N19'22.686 E98'43.272 and take the fork on the right towards the north. The trail is 4WD passable the whole way through, but there's one wooden bridge that might be "interesting" in a big truck. There are three river crossings but none were deeper than 18 inches or so when I did them. You'll get hero points from the local kids if you can ride all the way across without putting your feet down. There was one soft uphill section after the second crossing where I had a little trouble. My rear wheel kept digging in because the gutless motor of the clapped out rental bike needed lots of RPMs to get any torque. As soon as it got enough power to get going, it would spin the wheel and dig in. This was with pretty good knobbies on the bike. If you're on a big bike or have dual sport tires (or worse) you might want to have a friend along to help push. It's definitely doable, but will just take some time. The trail after Huai Ya Sai led me to Wiang Haeng where I stopped for gas (N19'33.390 E98'38.550). This is somewhat different than what's shown on the MHS map, which shows the trail hitting 1322 much closer to Mae Tae. Perhaps the road has changed since the map was made or I was simply on a different trail. From Wiang Haeng, follow 1322 east to 1178 and then south to 107. I suspect this part of the loop is quite pretty too, but I rode it at night and didn't see very much. The whole loop starting from and returning to Chiangmai is about 300km, so leave early in the day unless you want to do a lot of night riding as I did. If I'd had more time, I wanted to continue west to Muang Noi and come back via Pai, but I'll have to save that for another trip.