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
How are you timing it? The worst way to time an old engine is with a light, as the vibration damper on the crank often moves on the rubber over time.