I just bought a 66 Mustang, 289, with a 750 Holly and msd ignition. I had it shipped over from michigan. When I start it it will run for about 20 seconds and then starve and die. I can have it at idle or revved to 3 grand and it will still die. It does better in neutral or park but as soon as I try to get it into gear the idle has gone top low and it dies. After it dies I have to let it sit or it is hard to start or only sputters. Give it a minute and it will start and run for another 20 seconds. It is a manual fuel pump. The clear horizontal fuel filter looks fine at 2/3 full the whole time the car is running and after, there is a sound of liquid trickling for maybe 7-10 seconds after the car dies(maybe fuel returning to lines or air escaping lines??). Could this be a vacuum leak, carb issue or fuel pump? what order/how should I go about testing these issues. Thanks!