[jonathan180iq]

We all are fairly fond of Seafoam or Berryman's B-12 Chemtool for maintaining a clean carburetor. I also am partial to Marvel Mystery Oil, but I'm kind of a weirdo. (Might want to buy a can of the pressurized stuff too, just to have at your disposal.

The remnants of a black or brown substance on the petcock side of the engine is very common with these bikes. Clean it off and monitor it to see if it returns or how quickly it grows. It may very well be nothing more than the left over shipping oil that was put in the bike when it was new. Seems like every single GZ owner has seen that smudge.

How much choke are you using? In weather that cold, you're going to need full choke. That's normal.
You shouldn't have to use PRI to start the bike, ever, unless it has been broken down and you need to refill the float bowl.
Is it possible that you just THINK you need PRI and you really don't? If you actually need it, then you have a vacuum issue, where the engine pumping isn't sucking the fuel through the system... OR you have a dirty carb, as you've already suggested.

Since it's the winter anyway, and this season is hard on a bike, I would take the time to check the condition of your vac lines, get yourself some carb cleaner and spend some quality time with her. These things are so simple to work on, and there isn't a whole lot that goes wrong with them. The few things that are common, we all know how to walk you through. You'll get it sorted.