2000 blaster completely stock with a uni filter. stock jets has lid on. good power up until higher rpms. hits a wall , starts to bog. the previous owner said his son was tinkering with the air/fuel mixture screw. could this be a contributor for the reason why it starts to bog when i reach higher revs? not getting enough fuel? havnt had a chance to check the plug, just trying to get a couple suggestions where to start.