Bocking and jerking

Hello, 14 days ago I bought a Ford Escort VII GAL 1.6 i 16 V BJ 12/94 65 kw 88 PS 92,000 run. after about 2 days the cooler water tank ran out …I called the dealer he said: If your bad luck they should have had to look better they sold them as a hobbyist vehicle. But they agreed to repair me the timing belt and the water pump for 280 €. he then drove about 2 days great and since then he jerks and bucks without ending and jumps first nac h the 2 – 4 try at…first I thought it was because I have super fueled …but a known one said it couldn’t be …can be related to the installation of the timing belt …have a 1 year warranty. Only before I go there on Monday and test a mega (because I’m getting enough with the dealer) I would like to know if maybe one of you knows what it’s related to …have fueled again but he’s still banging as soon as I’m a little m thank you for your help LG Bianca