Hello all, I am new here. I’m 16 so I don’t have a lot of experience nor tools. I got a 66 mustang for my 16th and have run into some issues. It’s a modified 289 with a c4 auto transmission and a Holley Performance 2 barrel carb. It wasn’t idling last Tuesday and I managed to get that fixed but it started misfiring badly with backfire too! It has never done that. We had a friend come look at it and said to check the timing. Unfortunately I don’t have the knowledge to do so so we were going to take it to a shop. When I put it in reverse on Thursday, it started accelerating on its own. At first I thought it was the throttle that had gotten stuck but it only seems to do it in reverse. I’ve talked to my family which is made up of people who love cars and no one seems to know what is going on. Looking for some help. Thank you.