We are laning in in Wales these days, this forest though is something else, it's not like your normal quarry play sites. Don't get me wrong there's plenty of challenging stuff, mud etc etc but there's normal lanes as well.. Views, camping etc etc
If you are running 100% oil,it's most likely that's it, mine did the same. The oil turns into thick sludge when cold and the pump just can't shift it. So it needs to be thinned down, diesel or petrol.