Had a proper listen now. Plus some help from a guy in Rjukan, Telemark, who I go ice climbing there with! It's an old Telemark dialect, hardly used any more, according to him, and he had to get his granddad to listen too. However:

I Vinje sokn der hugen hutar,
og kjempekarar og gasta gutar,
Men då på vetteren er god si tid,
På Kongsbergmarken der gjeng en fri.
(Unclear line)
Og bøgra ligge på hoge hampar,
Og gutan er liksom grautestampar,
Deg kinnar upp og deg kinnar ned,
Og styvne er deg og ende te.....

Loose translation:
In Vinje parish the men and boys are waiting for the Kongsberg winter fair (market, literally, but as Shimmering says, the Kongsberg Winter Market is something more akin to a fair). Because then they have time off and are free to do as they like. (Unclear line). (Someone) is laying with high expectations, but the boy is acting like a porridge stirrer ("masher" would be more literal, but I've never heard of a "porridge masher" in English!). Making movements up and down. And he still has a hard one....

(My friend's...and my...understanding of the last bits are that it's all related to...probably unfulfilled... sexual hope and expectation).