Try adjusting the H and L screws in a bit, if your needle adjustment is off, you can compensate with the jets. I had the same problem when I did one, first try had to have them both out almost 2 full turns. Second try after bending needle fulcrum, both had to be about 1/2 turn out to run good. Third try was a charm, split the differance, and all was well.
Needle adjustment on these carbs is critical, that is why they are able to run in any position. That needle valve controls fuel at any angle. If I remember b.(again, had a few brews) the top of the fulcrum lever should be around 1/16" or a little less from the top of the carb. Lay a straight edge across it, Check it.
I took mine apart about 3 times and adjusted that before I got it right.
If it is running too rich, try turning both screws in about a half turn. If things improve, you are getting too much fuel through needle valve. Bend the fulcrum lever down just a hair, it is touchy. I did this process until the saw ran great at about 1 1/8 turns out on both jets. This was on an Walbro WT16b. Make sure all passages and screens are clear, did you change the fuel filter in this? Fish stresses the importance of this, I can vouch for this. The old filters had a foam type filter inside them, after several years these fall apart and wind up in your carb. Plugging up important holes. Try turning the screws in, if things improve, most likely the needle valve is letting too much fuel in. Or you could have pieces of that old filter clogging it.
These are very simple carbs, but they have to be adjusted correct, and they have to be clean. Good luck, keep us posted on results, we will figure this out.
