I have a 79 GMC 1/2 ton pickup with a 250 straight six that I purchased a while back for my son as a project. I was told by the previous owner that the truck wasn't driven for at least a year and was only started once or twice during that time. The engine runs rough, but doesn't smoke or knock. I checked the timing and noticed that it was at least 30 to 40 degrees below top dead center (BTDC). When I adjusted it to around 8 to 10 degrees BTDC it ran even worse and would backfire some and would hardly crank. It has new plugs, plug wires, distributor cap, rotor, etc. What could cause the timing to be so far out and run smoother than when it is timed properly? Could the distributor have been previously put in and be off a tooth? I'm basically trying to figure out whether the engine is worth messing with. I had planned on putting a 350 in later, but would like to leave the 250 in for the short term until my teenage son proves he can stay out of trouble. I only paid $225 for the truck, so a new engine wouldn't be a major setback. Any help would be greatly appreciated. Thanks.
Chris