I have a friend that did the same to a prelude. The computers in hondas are very basic and do not cross check them selves like Audi or such. the fuel enrichment (pulse width) is learned for one setup , when you change it, it is still for the original setup, when changing cfm and backpressure you push fuel through the engine at a higher rate. causing unburnt fuel (black stuff). if resetting the comp dont solve it, change map sensor manifold vaccuum to the closest fitting line to the head and add a delay valve inline. if those two fail back your timing (retard) a degree at a time and try it step by step. everyone says advance for power. but, when you mod you must retard, as it is much much more efficent with higher rpms at a load .