ok so I took my truck out after about 2 years of not being driven on the street. (it was started and moved from time to time) Well it runs pretty good but when I get on it at 1/2 throttle or more it starts to back fire through the carb like crazy. Like i said when I parked it, it worked fine and we did start it a few times to move it and all was well. The only thing that appears wrong with it is I need to adjust some of the rockers as they are making a bunch of noise, but I don't think that pertains to this problem. 454 in a 49 chevy p/u with a th400 and a 10bolt with 3.08s thanks Brent oh I have tried adjusting the timing from retarded to advanced and it makes no difference.