How do I adjust my Poulan Weedeater GHT225 carb for running at high speed?

I have a weedeater GHT225 trimmer which ran fine the one time I used it last spring 2007.

It will start right up now however it will not run at high speed RPM's. A fresh mixture of gas and oil was used with the same results.

I read on a website it could be the spark arrestor limiting the RPM's. The spark arrestor in the muffler had no carbon build-up however I cleaned it with no improvements to the high speed RPM's.

Next, I carefully took apart the carb and soaked it in carb cleaner overnight with the same results.

It seems as if the high speed needle needs to be adjusted (opened) so it runs at high speed. If I set the choke halfway it will run at high RPM's.

There are two black knobs on the side of the carb which looks as if should be the low and high speed adjustments except they look as if they are pressed into the carb.

My question, is this carb adjustable or is set one time at the factory?? If it is adjustable, how is it done?

Any info would be greatly appreciated.