Just an update for anyone who might be reading this thread: I completed the route (BR230 East to West - Maraba to Humaita, and BR319 South to North - Humaita to Manaus) over 9 days, from 16 to 25 August 2010, solo, on a standard KLR650, with two rest/repair days. I didn't camp at all.
So, a run down, the BR230 is a good surface (there was very little rain, otherwise there would have been quite a bit of mud to negotiate), but it's long, and the dust thrown up by the numerous trucks is hazardous and uncomfortable. I wiped out overtaking one of these trucks through a dust cloud and didn't see an oncoming truck until it was about 5 meters in front of me. Ducked to the right, but couldn't stay on the bike.
You can generally ride at around 80-100 km/h and I managed one 700km stretch (from Apui to Humaita) in one day. There's only one bit where the sand is deep and loose in patches (between Itaituba and Jacareacanga (after the Amazon National Park), but that lasts for only about 30kms. There are quite a few spots with roadworks underway. No broken bridges, no washboard stretches and about 5 or 6 balsas (barge/ferry affairs to take you across rivers). It's all dirt except for a few 10km stretches before/after one or two towns.
The road between Maraba and Itaituba is much more developed than what comes after it, and there are more petrol stations, places to stay and restaurants. From what I could see, the deforestation and development in this stretch must have happened quite some time ago, so the "urbanisation"/populating process is quite far along. Not that any of the towns (other than Altamira - which has an HSBC! - and Itaituba) are very big.
After Itaituba comes the remote and forested National Park, and after that there are large gaps between populated areas - probably around 200kms of nothingness on average. The deforestation process is continuing at a tremendous pace - the smoke from the burning forest was overwhelming for a good 800kms!
While the BR230 is a good challenge, it's not the lush green Amazon experience that you might expect it to be.
The BR319 is very different. First of all, I did check with a good number of locals before I tackled it, and I would strongly suggest that anyone else who wants to ride this route do the same as it seems as if conditions can change radically from year to year. It does, however, looks like they're gearing up for a redevelopment of the road, so conditions may continue to improve, but I would still advise obtaining local advice.
The road surface is shocking. Not too bad for the first 150kms or so from Humaita (the first 60 or so are perfectly paved and then for another 100kms the road is fairly even). It then gets very very bad for about 350kms. It seems as if the whole road was paved at some point, but it hasn't been tended to for decades so there is crumbled paving all along, making it very bumpy indeed. Depending on how much you want to bruise your bike, you're probably looking at an average of 30-40km/h for this stretch.
ALL THE BRIDGES HAVE BEEN REPAIRED (FOR THE MOMENT). It looks like they can pretty easily be broken/warn down with heavy traffic though so, again, check before you go. Some of them are a little shaky and require balancing on some narrow planks, but nothing too hectic.
The last 200kms into Manaus are fine. The final 100kms or so is a good paved road and before that the paving is a bit patchy, but you can generally do around 60-80km/h.
Gas - still nothing for around 550/600kms from Humaita (pardon me for not having the kms exact, but I broke my front hub in the accident and couldn't reconnect the odometer when I replaced it) until you get to Careiro. There are at least two big petrol stations in Careiro.
The difficult access means that there is very little deforestation along the BR319, so on this bit you get more of a lush Amazon landscape, which is refreshing after all the smoke on the BR230. It also means that there is very little habitation. Especially in the middle part, there must be around 300kms where there is no sign of human settlement at all. So if you get stuck, you'll have some difficulty, BUT, there was quite a bit of traffic. I passed about 5 trucks and one bike coming the other way (I did the BR319 over two days), and I passed two trucks going in my direction.
There are 3 spots on the BR319 where you need to catch a balsa. All three are in the final 300 or so kms of the road.
As I mentioned before, it looks like they're gearing up to improve the road: there are two concrete bridges under construction, and there is a camp for a road crews set up. So, signs are good for an easier ride in years to come, but bad for deforestation, I would imagine.