Those are limiter caps put on every carb on every small engine sold in the United States for the last 7-8 years. It is part of the EPA emissions requirements which forces the manufacturers to set the carbs on the razor edge of lean and then put caps on the adjustment screws to prevent an owner from easily richening it up. The EPA does not care if your saw burns up, they only care that they stop the 2/1000000 bits of unburned fuel from escaping and destroying the Earth as we know it.
In the real world we just take a razor knife or diagonal cutters and snip the tab off the cap to allow full adjustment. The caps can be removed but they will likely be destroyed doing so and they should be on there to hold the adjustment, otherwise the screws can back out from vibration. Or you can get new caps from your dealer after you destroy the old ones and set up the carb so the saw runs properly.
Wow, it's been a while since anyone has come in here and not known what the limiter caps were. It's cool though, any more questions just ask.
