Imma just throw out sorts of power scaling with this (None of which is confirmed at all, so dont take anything seriously.)
Goku without his tail is around Krillins level, a power of 80-90
With his tail he becomes as strong as Roshi at about a power of 120 (If not slightly stronger, but still loses due to his height difference.). Roshi went into the tournament knowing well he could beat Goku at his level, but once he regrew his tail and got stronger, it was a lot closer of a fight. This also work with him beating Nam who is stated to have a power of 100, someone who is a highly trained fighter and more experienced than Goku at the time, as well as being older and living in more harsher environments.
Yamcha was able to wipe even the best Martial Artists in the world and secure a spot in the top 8. I would place his power around a 40-50 ish seeing as he worked his ass off to try and keep up with Goku, but since he did it alone without guidance, Goku and Krillin outshone him since they trained under one of the strongest Martial Artists of all time.
Putting it into perspective, Yamcha is one of the strongest there and was really lucky people like Pamput or King Chappa didnt show up that year. Once he trains with Roshi he would see incredible Gains like Krillin and Goku did.