Hello, I am having trouble with my engine not accelerating well when I give it full throttle. It seems to just studder to a gradual increase in rpms. Sometimes it will even backfire out of the carberator if I jump on it to fast. Could this be a timing problem. Does anyone know what the timing should be. It is a 68 350 camaro 4 speed with HEI . Not sure if its stock or built. Thanks