Chainsaw Repair

8000p, had the largest carb and hopefully its still with the powerhead.  Walbro HDA-45 is listed as 16.7mm venturi but its much larger.  The hda45 choke bore is 22.5mm and throttle bore is 20mm.  You can tell this carb over the traditional hda as the casting is larger.  Walbro made that hda45 carb for this model only and since discontinued it.  Replaced by HDA-63 which looks to also be discontinued because the parts listing now shows the HDA-153?         

Your best bet on top end parts is the newest H/O quad port cylinder and piston combo under part number P050005320.  If you shop around you can find it for $150, includes cylinder, piston, rings, clips, wrist pin bearing and base gasket.  Otherwise, a flat top piston alone is available under part number P021005420. 

This would be a good time to split the cases and replace the bearings and seals when you upgrade the top end.  Flywheel air gap is .020-.025.  Like cut mentioned, use a business card to set the air gap. 

There are two different ignitions used on these depending on when they were made.  The modules and flywheels dont mix and match.  If your having trouble post some pics and we will help you figure out which set you have.