Heres another for all you tech guys out there. We all know that the bigger the cam (duration and lift), the more power we get out of the motor. What I can't seem to figure out is why these high lifts and long durations cause such a lumpy idle.

 

because they are high lift and long duration
More air not enough fuel cause rough idle. Take your idle up or tune that crap and add more fuel at idle speed.

 

Would richening the mixture at idle foul the plugs?

 

riching yes, but you are getting more air then fuel at idle. Just up your idle, idle screw to fix the roughness. Personally rough idle sounds cool (when there is something there to back up the rough idle).

 

With more lift and duration comes more overlap. With more overlap, you get increased scavenging at higher engine speeds but you also get reversion at low engine speeds. Reversion causes the charge to be pushed back into the intake during overlap.