Hi there,
No worry, totally normal not to see any real movement in the ammonia yet. The ammonia oxidizing bacter (A-Bacs) are simply not numerous enough yet for your tests to pick up what they're doing (although they are there and doing some processing!) It sometimes takes two weeks for the first dose of 4-5ppm of ammonia to finally drop to zero ppm, and once or twice we've even seen it take 3 weeks. After that though, ammonia will start taking much less time to drop to zero.
Any carbon you have in your filter will not be the cause of this part of the cycling process being slow. It brings up a good point though: Do you need carbon in your filter? The answer, usually, is no. Carbon is a "chemical media" and as aquarists we us it optionally in our filters for short periods, to accomplish specific goals. The most common uses are to remove medications, to remove yellow tannins from wood and to remove the occasional organic odor of unknown origin. Carbon only lasts 3 days, after which it is sitting there doing nothing and is ready to be removed and tossed. Carbon is considered to be a valuable tool for the aquarist but is better left sitting in the supply closet until needed.
The confusion about carbon comes from the fact that the retail business, both filter manufacturers and retailers, considers it, like salt and a few other things, to be a good little steady money-maker to keep things moving on the shelves. There is a bit of truth in the fact that carbon can "clear up things" sometimes and so they exploit that as much as possible, trying to convince new users that they should be buying and replacing expensive carbon "cartridges" on a frequent basis.
Carbon is a poor "biomedia" (sponge, ceramic rings, ceramic gravels etc. are better) but unfortunately it will indeed become the substrate for plenty of bacterial colonies and can cause a mini-cycle if its taken out after its become part of the overall biomedia of the total filter. For this reason its good to get it out of there early on before the fishless cycle gets too far down the line. It should be replaced with a better biomedia. Part of carbon's problem as a biomedia is that it tends to crumble, pieces getting smaller and smaller until they are like dust and as this happens they are carried out with water changes, taking their bacterial colonies with them.
~~waterdrop~~