I would check the basic's first like the timing, normal visual inspection of the cap & rotor. look for corroded cap terminals or rotor firing pin burned away. I'm not sure about your definition of stumbling whether it is a miss, no power or a bad hesitation.
If the timing and secondary ignition are correct then I would look to the carb. An 85 model Q-jet MAY have a power enrichment solenoid that could be at fault. It's on the (looking in) right top with a 2 wire connector. If it's just a bad hesitation on take off you could have the carb pump going out.
Other problems with power loss could be restricted exhaust.
On a vacuum leak you would have a high idle in most cases.