hey im new to this kinda stuff but here it goes lol

my 2000 scrambler 500 starts right up idles really good drives awsome full of power then about 20-40 mins into a ride it starts loosing its power/bogging when throttle is applied and its starts spraying coolant out of over flow bottle now i can come to a stop and sit there and it will idle great but if i hit the throttle it starts backfiring boggging this only happens when the quad gets warmed up like i said runs great for the first bit so my question is is it a head gasket ? can a head gasket cause it to bog when hot and spray coolant plz help i have no mechanic in my town so im stuck doing this by my self hopefully with the help of some one i can get it fixed
thanks