Modern Buddy

The problem is the engine will not return to idle quickly after blipping throttle. Stays at a higher rpm then slowly returns to idle. Impossible to set idle correctly. Checked diaphragm, #3, no holes, installed correctly.
Carb has been thoroughly cleaned.

Is there a chance that the throttle cable is sticking a bit? It can be cleaned, if that is the case.

Checked the cable and attaching parts on carb. Lubed all, functions as it should.

Sounds like the diaphragm is taking it's time returning to the bottom of it's travel. The diaphragm return spring is in place, right?

Yes the return spring is in place. Took it apart, reassembled per parts diagram. Everything looked good.

I did notice that the bowl vent tubing is missing. Don't see how that would affect anything though.

That's your problem. The vent tube on the bowl (smallish? elbow shaped?) is actually part of an emissions circuit, which is a straight shot up into the bore of the carb. It's allowing a vacuum leak, if it's just breathing air freely. Plug that vent tube with a rubber cap, or a bit of hose that's folded over and zip tied. Your idle should go back to normal.

Would not run with vent plugged. Good news: pilot jet plugged. Could not unplug, soaked in carb cleaner, used jet cleaning tool, no go. #38, where to buy a new one?

Would not run with that plugged, because your pilot jet is gummed up. Clean the jet with an ultrasonic and compressed air if you have access. If not, a new one will fix the fuel delivery, and plugging that vent tube will correct the vacuum leak.