Yes, the Pennzoil will help clean up the chamber but if it's real bad you might want to consider cleaning it manually. Like truckracer said, if the needles aren't set correctly it can be just as much of a problem as the oil. Partially burned fuel is left behind as carbon and it can certainly make the oil look like it's the culprit. I'm like tkg, what oil was it and what ratio?
I edited to add this link to another thread where I posted pics of nephews DA50. The pics of the cylinder and piston are after about 15 gals of fuel and that should equate to around 20 hrs of run time. It was on Redline Two Stroke Racing during that stretch and IMHO looks very clean. It had NOT been cleaned at the point the pics were taken. I wiped the piston off and reoiled it and put it all back together. He's still running Redline because it runs so clean. His is mixed at 40:1; I mix my Pennzoil at 32:1 and my chamber looks just as clean as his. The pics of his engine are in post #25.
http://www.rcuniverse.com/forum/m_9019552/tm.htm