The pilot jets on the PD42/b series carbs are only #35 and clog easily. Also, the PD carbs have those tiny O-rings above the tiny washer on the tips of the idle screws: if the O-rings break (from age) then the mixture goes dead lean at idle. I had a similar F3 here one summer that had 3 out of the 4 O-rings split, the 4th missing altogether (along with its washer) - it would only idle at 1800 RPM and needed choke to get up there.
I found all 4 tiny washers but no o-rings. I used magnetized bicycle spoke to fish them out.
The order is spring, washer, o-ring i assume.
It's unlikely someone would install the washers but not the orings, so they are probably compressed/stuck into the end of the barrel. Use some light to peer down the barrel and look for black rubber donut as opposed to shiny metal.
The orings are harder to get out than the washers, so you will likely need to bend a paper clip to create a little hook at the end and then fish them out. It will take a little time.
If you decide to buy replacement mixture screws (not always needed), check the length of the springs against the originals. I recently bought a screw and the spring was shorter, causing a bad seal with the oring and leaked gas out the mixture screw.
