Any info on a Hawk 250 dirt bike.

[Sub Dude]

Just bought this Hawk 250 dirt bike in Arlington Texas and wanted to get more information about it. The bike is from the Chongqing Haosen manufacturing company and has a 167FMM 223CC engine. Is this manufacturer known for quality products, I found very little information about them? Are all of the 223cc Honda clone engines basically the same except for the side covers? I had the retailer replace the oil with synthetic oil and drove the 50 miles home then replaced the oil again. I found very little debris in the oil screen and the used oil was dark but nothing I did not expect. I put another 100 road miles on it the next day plus 5 off-road hill and sand miles. So far the only issue I have with the bike is it only will do 50 MPH and acts like it is starving for fuel or has a rev limiter kicking in. Lower speed but hard acceleration will also exhibit the same behavior. If the manual is to be believed the bike should do 60 MPH. I have not run it with the fuel cap removed to verify proper tank venting yet but wanted to hear other ideas of what I could check the next time I take it out. Thanks for your help.