The usual culprit when we see an engine surging is the air flow jet. It becomes clogged with dirt, grass, and more plugging up the jet and restricting the flow of air for the air to fuel mixture jet to operate properly.
On your older carburetors, we need to enlarge that hole to allow more air in for it to function properly. We use a jewelry drill bit set (Micro drills) to enlarge the hole. A link to this is at the bottom and can be found on Amazon. No… we are not affiliated nor are we compensated if you buy one.
Hope you enjoy the video
Micro Drill Bit Set on Amazon: https://www.amazon.com/dp/B0C46BPQ53/ref=syn_sd_onsite_desktop_0?ie=UTF8&pd_rd_plhdr=t&aref=3Sm4YQoQRS&th=1
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Excellent video!