In my experience (mandarin, Taiwan), uncle was jiujiu, bobo, beibei, or shushu. I wouldn't be surprised if those were more colloquial names and I simply don't know the formal ones. Alternatively that's not mandarin. But I've never heard of kowfu or kumu.
edit: I should add that I'm using the standard 'pinyin' spellings of those 4 words for 'uncle', which cannot be read directly as if they were english words. Also note that while they all translate to 'uncle' in english, they don't all mean the same thing in Chinese since we differentiate between uncles on your mom/dad's side of the family & also between the older/younger ones.
When I say those sounds they sound like vowels to me? I did take linguistics years ago so I should know better. Maybe it's got something to do with hard/soft consonants, or voiced/unvoiced or some other distinction. But the way I pronounce "sun" (not at all similar to how english pronounces sun, the star at the center of our solar system) is nothing like my guesses for "kum" or "um". Like with that "m" you're actively forming the "m" when you say it, similarly to the "n" in the english "sun". But "ming" in Chinese is kinda similar to the "-ing" ending in english where you aren't explicitly forming the "n" with your mouth. If that makes any sense...