Engines run on air, fuel ,and spark. Fuel filter is a good start. Check fuel pressure too, as the fuel pump may be going. Don’t know if there is an intank filter fitted, but if you get something in the fuel tank, that filter will also clog. Second is the spark hot. The coil may have degraded. I there are points check the dwell angle, and that they are clean, and conducting well. Pitted/Dirty points could cause the symptom you’re having. A bad or clogged air filter could be the cause, but that should cause a noticeably rich mixture. Also be sure the timing belt hasn’t slipped a tooth. Because bad valve and ignition timing can cause bogging. this is a good primer on troubleshooting older engines that don’t have everything run by computers. https://www.hemmings.com/blog/article/the-lost-art-of-diagnosing-engine-problems/
