Another idea came in to my mind: what if you put under the carburetor some sort of a fixed turbine, propeller, or something that creates a vortex, that helps vaporising the water, so that the tiny droplets will not short the sparkplug.
Maybe another device like that must be developed to do the job.

Or, how about using this:
http://www.mainlandmart.com/foggers.html

Shanti  : I was thinked exactly the same of you..
The frecuency of the inverter must be superior to 50 or 60 hz for
good response at high's rpm.

Look this schematic about a modern CDI...(read the explanation) use mosfets at high frecuency for a
good response of the "inverter"  at high rpm and multi spark :

www.molla.org/DIY-CDI/SC-DIY-CDI-article-hires.pdf



I hope this serve.

Yes, a fogger is a nice device, but then you should feed the engine directly in the manifold, avoiding the carburettor.
Carburettors use only liquid fuels. Its job is to vaporize this liquid...

pablitosax and Shanti, you are right.
A big capacitor needs high frecquency to be charged quicly.
A good CDI uses high sonic or ultrasonic frecquency: 20KHz-50KHz. That is why I suggested to use an 555 oscillator instead of the inverter.
It takes only 31.8microsec (0.0000318sec) to charge a 100uF capacitor at 350V, using an oscillator that runs at 20KHz. Think about that.
That PDF presents the "John Clarke CDI". Two, maybe three of my friends in Romania tryed it, and it worked very well, giving more horsepower and better mileage.