recently bought a 1982 xj6 for 500 dollars. instantly i thought deal and snatched it up . he said it needed a engine rebuild but seemed to run alright low speed. i payed him cash a couple days later and took off. on the way home though it wouldnt get up past 45 and pedal to the floor it refused. until after about 15 minutes then it kicked in and ran like a champ. are the fuel lines or injectors clogged.?