I'm not sure where a factory fuel filter would be on your car. My filters are non-standard.
When does the car misfire? While it may be fuel related, always tackle electrical tuning first before touching the carbs. Resist temptation. The points on the A-series engines tend to wear and close up quickly. Be sure to check and set the points gap. If you have access to a dwell meter, it's often better to adjust the points using the meter. Once you've got that sorted, move onto setting the timing. You may be surprised at how much better the car can start and run with just those two adjustments.
Prior to setting the points and timing, be sure to check the condition of all the electrical components. Start at the spark plugs and work your way back to the distributor replacing anything that looks suspicious. When your working with the points consider replacing the condenser "just because"... but save the old one as a spare.
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Doug L.
'64 Morris Mini Cooper-S 1275
'67 Triumph GT6 Mk1
'72 Spifire Mk4