I am going through my pony carb and have a question about the main jet on my zenith carb. This is a carb off of my D8 !h. IS the opening at the top of the jet supposed to go all the way through to the opening on the side of the jet? Mine doesn't but I just am not sure if that's how its supposed to be. 

Are you talking about the tip? I can't recall but likely. Do as I mentioned about the wire and spin the jet a bit. If you see black crap coming out, you know that is crap that should not be in there. Very likely there is an orifice that needs opened. Absolutely never use a drill bit or anything similar. Not even a tiny screwdriver. The wire works.

I tried the wire and it would not go through. it felt very solid which is why I am wondering if it just doesn't go all the way through, but then I don't understand why the end is hollow if no fuel is intended to pass through it,

Just to state the obvious here, they went through a LOT of trouble to blunt and hollow that center and cross drill so you can nearly bet there is a passage there. It can be really difficult to troubleshoot a carb without having it in my hands, but I can guarantee you, you have a lack of fuel delivery on the main jet. I'd write that check today. Let that me your motivation to get the fuel issue resolved.

I will say this, I have been in countless carbs where "pros" have been. It means very little to me because if someone does not know what they are looking for, they just polished the same turd.

that passage probably has not worked for a LONG time. This is usually where people just give up and buy something else. I usually don't because if it is a knock off, who knows if it will work right. As well, others have probably went to turning that jet handle. The way they are dialed in is from the seated position. 2 turns out, ,3 turns out, etc. That should have been recorded before tearing down. I say this because people get to turning and then you have to get back to a baseline. Usually 2-3 turns on about anything is close enough to run, then let ears of experience lead you.

soak it in a plastic jar of shellite or carb cleaner for a few days and try again. give the jar a occasional shake. you can also try having it sonic bathed your local mower shop should be able to do this for you its much gentler than poking around with bits of wire.

I tried using a fine thread needle and was able to get the opening unblocked. So hopefully that will help it run better. Now to just get everything back on the pony, because in order to pull the pony head I had to remove the right half of the main engines exhaust manifold, the pony manifold, and the coolant pipe. Some of those bolts were near impossible to get a wrench on.

yes they can be "fun"