I got a mercury Monterey recently the timing was set to 2. I set it to 6 and also adjusted the choke, mixture screws and idle screw and it ran smoothly for the whole day. Come the next day as I try to start it and it just cranks. I've checked the spark plugs/wires, cap/rotor, ignition module, and coil but they're all getting voltage. I went through the carb again and no matter the setting it won't start.
Don't mean to question your level of knowledge, but here's a few things:
Was the vacuum advance hose pulled off of the distributor and plugged?
Was it reconnected and the hose in good condition? I've had hoses that looked fine until I pulled them.
Is 0 truly 0? To verify, I've pulled the spark plug and made sure that the piston was at the top of it's travel. I've seen the harmonic balancer indicators be off as much as 5 degrees.
Ever notice that there's so many high performance parts available for GM products?
What did you use to carry out adjustment to mixture , choke settings etc. ? or was it just " by ear " ? If not set correctly might be over / under fueling .Pull plugs and examine , might give you a clue of what's happening .