I have a Pb-200 which is about 3 years old and has lost some power. So I picked up a Pb-251 which has 390 cfm at the tubes while the old Pb-200 has 305 cfm at tubes yet the old one blows better? They both say 145 mph. Any ideas why the new one sucks? Is there a break in period? Do I just take it back and spend the money on a stihl?