Definitely check your engine before shelling out $ for a new cdi unit... even tho this type is still only about $15, unless you want to have a spare just to keep on hand, which can be a good idea anyway...
You could probably make the cover into a "hood scoop" by opening up the front on each side of the bolt that holds it on. If you do this, you could remove the little fan blades off the rotor and drill a few small holes in back of this cover so air could flow in from the front and escape out the back of the cover. The fan may prevent fresh air from coming in if it wasn't disabled or removed using the "scoop"method.
The idea I came up with uses the fan to sucked air in from a hole in the cover and it'll force it out of a series of holes up front, the fan set up this way should easily be able to overpower the "ram air" even at 40mph and above since the fan will be able to pull in the fresh air from the hole right above the center of it, basically this would use the fan as a centrifugal air pump which would work at idle and become more effective as rpm increases but I needs somewhere for this fresh air to escape once sucked in, which is why the holes up front are needed, and also to direct the cooling air over the cdi unit.
I've seen someone using a billet cover on this type engine where they just cut slots between the fins for fresh air to enter and hot air to escape, this is another passive way to get some air circulation and because of the fins on the billet cover the slots cut between the fins are very inconspicuous, which could be good if building a custom engine....