Cylinderfot gasket on a Big Bear

[Yfm350fw]

Hi, the cylinderfot gasket on my Big Bear 350 -92 (4-Stroke, SOHC) is leaking some oil and i was woundering, is it difficult to change it yourself? Also, when the engien runs on idle i can feel like small "hits" (spec. when its cold) What might it be? And last, when i put full throttle, from idle, the engien dies. You have to give som gas first, then its ok to give full. Is this normal?

Thanks for any help!