I'm doing an engine swap from a 305 to a 350 carbureted. The motor is in, turns over and runs. It had a rough idle, and sputters and nearly dies under load unless I baby the throttle. I'm at a loss of what the problem is. Fuel pressure is right, there is no issue that I can see. Adjusted the idle to smooth it out bit is still a little rough. Once the truck is in gear though, you can clearly hear that it's fighting to stay running. Everything about this motor was fine in the truck it came out of. Started, drove, idle was fine. It's a strong motor. Help please!