always start walbro carbys ,screw both screws in till just done up then take out 1.5 turns saw should start then use high speed screw to optimise saw at full revs the low speed screw is for when you give throttle a quick burst so optomise the setting to get no delay in sudden bursts of throttle I think this should solve problem use idle screw to adjust revs at idle
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix chainsaws.