I live in The Gambia and have traveled in Guinea, but not recently.
There are traveler's advisories for Guinea but also for northern Mali, including Timbuktu and Gao.
Be aware that when you enter a place like Guinea at this time there is no law. You may be fortunate and encounter nothing more than an "odd drunk soldier" but there is no central control in that country right now. This means that the soldiers at any given checkpoint can and will do what they wish. The only restriction on their behavior is the whim of the officers at that particular check point. Guinea has had a history of decades of totalitarian rule and it shows in the behavior of the soldiers and police. Even when the former ruler, Lansana Conte, was alive control of outlying garrisons was poor and many soldiers and officers did what they felt like. This included very aggressive demands for money at military checkpoints. The chance of being shot or arrested is probably low.
The Guinean people themselves are terrific: kind and hospitable. I am very sad for their country.
You might want to reroute through Burkina Faso. You might also want to ride with at least one other person, if possible.