petrolheed

Hi Folks, new to trials and new to site... need some advice pls. I have a 2002 280 pro and all seems good apart from the front forks, they bottom out when dropping off an obstical or when dropping the front wheel. I had a go on my friends 05 gasser pro and the front end felt great. SO, the question is - how much fork oil do i use in each leg and what weight oil ?, i'm a big lad at 15 stone so would 5w or 10w be best for the job ? ... also the blue and red 'knobs' on the top of the forks, what should they be set at when chainging fork oil (what do they do ?). Thanks for any advise guys. P.s. fork seals seem good