I have tested some of the the GRpro engines range, and found especially the 26cc lacking. It puddled fuel in the crankcase, so the engine would sag badly on any attitude change. Starting is excellent, and so is the ignition used. So I tried to rebuild the engine to side carb configuration. Still the same problems, and quite low on power. All as of status may 2007. With this engine, I got quite a bit less than I paid for. Even so much less, that i decided not to bother and invest in time/effort any more. The best engine in the range was the 45cc with side carb. After rework, it was an excellent performer.
The design may have changed that I do not know of, so ask questions and return warranty before you buy.

@ soarich:
The engines from the shanghai engine valley area are by no means all the same. Some sellers work extremely hard to get their product ready to perform as required by today's market satandards. Copperhead is one of them. He has folks over there to watch over all deliveries.
It is sad to say, that there are others, that sell engines at large profits without investing in any form of quality control and backup services. In between there are shades of grey.