Does sugar intake cause excess mucus in gut?

Not usually. Mucous is produced by your gut in order to move the byproducts of digestion more smoothly through your intestinal tract. Things that irritate your intestinal lining will cause the production of more mucous. Like infections or inflammatory bowel disease, ingested toxins can do this and possibly reactions to food items that your body is sensitive or "allergic" to: sugar alone isn't likely to do this.