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1986 Toyota Pickup - Stumped

Just replaced the timing chain. Guides were broken. Before this, I was having trouble with my ignition timing. I have the 22R sohc, carbureated. I have good engine vacuum and ported vacuum to the distributor. Above 2000rpm the engine retards, instead of advancing causing it to fire with the intake valve open backfiring out the carbureator. What could cause timing to retard? I replaced the pickup coil, vacuum advancer, ignition control module, coil, plugs and distributor. I am stumped.

Do a leak-down test on the cylinders to check if any of the valves are bent.