How to retime the timing on my engine?

I have been driving my 1994 toyota celica for about a year and a half now since I bought it and I have had one
accident with it but it was only physical damage and from the crash my water pump cracked along with the radiator.
Which means I had to replace both and about a couple weeks ago I had changed my Water pump and timing belt
because of the crash and I have started to notice now that every time I go to accelerate the vehicle the car starts to
jerk as if there is not enough power and back fire on me from about 1000rpms to about 3500rpms. And the
situations has been getting worse since then. I have spoken to many car experts I would say and they have all given
me the same response. Either it's the type of gas I am using or it's my timing marks that are misplaced. I need to
figure out how to retime my engine. And very soon because this is the only car I have to get around with. Please let
me know what you think and what I should do. Thank you