mk2 breadvan behaving badly

i have had my mk2 1.0l for about a year and a half but i've only been running it for the past couple of months because i have been in france for the winter. i drive it from essex to hull every weekend and since my brother borowed it its not been running right

i left it for my brother to borrrow while i was on hols and he rang me up one day and said it was kangarooing and it had no oil in it so he filled it up but he over filled it, so when i got back i got rid of the oil and changed the oil filter and oil and ran it up to hull again then when i got 20 yrds from my girlfreinds house it started doing it agian but this time it splutters and stays on the same rev when i put my foot all the way down on the accel i need help asap as i am stuck in hull as it doesn't go faster than 30 lol its sounds fine when its idleing and doesn't splutter when you rev it its just when I'm moving please help