I have a 66 Mustang 302 that I haven't been having any problems with. However, after having run out of gas, I noticed that when putting a load on the engine...it tends to vibrate heavily. The vibration "feels" as if it is coming from one side....Im not aware of any knocking sounds or anything else of the sort. Additionally, after the car has picked up momentum.....the vibrating diminishes and is not as heavy when I put a load on it. Anyone have any thoughts on what it might be?