Good day all,
Just snagged a 1987 MM, 2.6L 5sp. Hauled a motorcycle with it the first day, despite it misfiring like crazy above half throttle or so. As I'd expected from reading here, the secondary actuator wasn't holding vacuum, but the linkage was also installed incorrectly so it couldn't turn more than an 1/8th or so not matter what the actuator and interlock were doing. Both those issues are fixed for now, although my diaphragm repair is definitely not for the ages.
The previous owner did a little bit of maintenance to it: cap, rotor, plugs, and fuel filter were done recently He also disconnected the EGR system in an attempt to get it run better. I also found receipts for rebuilding the carb and setting base timing in the last couple months, but I'm pretty skeptical of both of those being performed properly, if at all. I did wires, air filter, PCV valve, cap, & rotor since I got it, along with new carb base and air filter base gaskets when I put the carb back on. Trimmed a couple vacuum hoses and replaced a couple vacuum port plugs that weren't in good shape.
It runs a bit better now, although it still misfires when I venture a bit too far up the RPM range. One possible clue is that the fairly new cap had scorch marks to the counterclockwise area of each post. We'll see if it happens to the new cap also. Judging by rotation I'm thinking the spark is sometimes being forced to jump "forward" from rotor to the cap, which would get worse if the timing is advancing with RPM/load. Is my thinking right there? Try disconnecting vacuum advance and see if it gets better as a quick and dirty check?
Other work I'm planning, in no particular order:
-set base timing
-check for vacuum leaks again, and verify hose routing
-throw new O2 sensor in
-verify spark strength with inline tester
If time allows I'm debating putting in a Ford CFI 2 barrel throttle body I snagged off Craig's List a bit ago. Maybe some GM waste spark coils with a crank sensor too, we'll see. For now I'd like to get it running a bit better stock.