Take the air filter off when fogging the carb

Fogging oil through the carburetor intake works, and yes, you should remove the air filter first. The whole point is to coat the cylinder walls, valves, and crankcase with a protective oil film so moisture doesn’t cause rust over the winter. The air filter just blocks the spray and keeps most of it from ever reaching the engine.

Here’s the standard method: run the engine, get it warmed up, then take the air filter off. With the engine running at a fast idle, spray fogging oil into the carb throat in short bursts. The engine will start to smoke and stumble; keep spraying until it stalls. That tells you the oil has made it through the combustion chamber.

For extra insurance, pull the spark plug and give one or two quick shots of fogging oil directly into the cylinder. Crank it over a few times with the plug out to coat the rings, then put the plug back. That’s not strictly necessary, but it’s the difference between “I probably did it right” and “I know it’s protected.”

One note: if you’ve got a fuel-injected engine, there’s no carb to spray into. Use a fogging kit on the intake, or add fogging oil to the gas/oil per the manufacturer’s instructions. But for a plain carburetor small engine, your plan is right — just pull that filter.

This is a ten-minute job, and it’s the cheapest insurance your engine will get all year.