250 engine timing

[jfw432]

Hey guys, new here and just bought a 79 C-10 with a straight 6 250. I've been looking all over the web and it sounds like timing on these engines should be fairly straight forward. From what I can tell, there are supposed to be sawtooth marks on the timing cover. However, this truck has no timing marks from what I can tell.

Here's where I am... I disconnected the vacuum advance and the engine sounded more like 1500rpms vs 2500rpms (no tach here) and barely running. It looks like the timing marks should be on the timing cover on the drivers side of the engine. I've cleaned all the goop down to bare metal on the timing cover and it looks like there is a nice flat section on the cover with absolutely nothing on it. From what I can tell, passenger side is advance (BTDC) and drivers side is retarded (ATDC). The engine was timed way on the drivers side and ran very poorly especially when cold. It basically required that 2500ish rpms to stay running.

I did what I believe to be advancing the timing until it's a little past center of the flat spot on the timing cover on the passenger side. Had to lower the idle screw significantly. I kept adjusting until it sounded like the engine rpms quit going up and then tightened the distributor back down.

Does this sound reasonable or is there a better way to ensure the timing is correct? Or am I missing something entirely?