1986 F150 keeps shuting off and backfiring

It's old with some miles and I can relate to that

TMK these engines are good but had problems with head bolts that are one time use turn to torque which caused some strange problems. If still original the timing chain needs to be checked. Same tricks as any - many used nylon cam gear that doesn't age well and can jump. Check for how much "lash" it has by turning crank bolt at TDC and watching distributor's rotor. Note that much more than 5 degrees it means trouble. If OE and a keeper just do that stuff.

Late carbs by any maker were a problem. Stuff on the vintage is fixable and durable so decide on invest some or give up based on overall condition. They rusted badly here fast so not many around now. What do you want to do?

T