HOW did you turn the idle down, via (1) mechanical butterfly adjustment screw, or (2) idle/pilot mixture screw?
If (1) no rational explanation, coincidence, probably "will come back", if (2)a possible explanation
However, smells here or not, what counts at the end how your gas mileage shows clearly that everything is OK. If its mpg fell into the 40's and even the lower 50's mpg it does indicate a poor running Kymco G/V engine.
PS: MaryK: I like your idea of the stuck float bowl; I had that on one motorcycle and had similar symptoms like "mverps" G/V. However, at one point it poured out gas when driving, so it was VERY obvious what happened. Sometimes fuel additives can help to get rid of impurities in the carburetor, or better soltion, taking the float bowl off, or draining it if it has a large bottom nut, and cleaning out any possible impurities.