Have an older blower, PB2100. May need a new carb. Searching online I see 3 choices. It appears that Zama OEM has a Hi & Lo adjustment screw but two aftermarket units may not have the Lo screw. The one on the right has a slot for a screwdriver but the middle one does not. That middle, large-headed screw, on certain Echo/Zama's, has always puzzled me; From other manufacturers, I'm used to seeing a Lo & a Hi etched on the body with "L" & "H". Not looking for advice of whether or not to buy OEM vs. A/M (OEM is really $$$ & this is an old, but decent blower). Anyone own either of the A/M's & can shed some light on whether or not one can adjust the LO side?