defo as Karl @ NMS is only up the road from you ill just take it up to him and get him to sort it out. I had the same problem and since i wasnt too clued up Karl sorted it out and its been great since (though it turned out to be the fricken crank sensor which decided to come lose and mess up the GAP)

If you cant sort it seriously dont mess around just go see Karl you cant go wrong

Best of luck

rk