TIming issue?

I bought a 87 nissan pickup. It runs badly, has little torque, wont idle, and seems to run rich. It backfires sometimes when starting or off throttle.
I found the timing was cranked all the way back to fully retard. I got a timing light and tried to set it but it only runs worse when set to the correct spot. The more I cranked it back the better it runs, till I reached fully retard again, and it runs, not great but it runs. Obviously the previous owner did this on purpose. Any ideas what would make a car/truck run better with incorrect timing such as this?

Possibly your valve timing is also off as well. I believe these engines used a belt to drive the camshaft, which may be worn and has skipped a tooth, causing the timing to be retarded (late).

If the valve timing is late, assume the belt is worn and replace it.