As suggested, adjust the valves, also test the glow system, one or more dead plugs makes these no fun at all to fire up. As will tight valves. (617 engines tend to tighten the exhaust's in the winter and intakes in the summer for some reason)
If you determine the glow system is ok, valve lash is right and fuel filters and fuel quality is good, run a compression test.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.