When removing, dirt usually falls off the pad and ends up inside that rubber pad holder. So before putting the pad back, use a Q-tip to clean the area where the pad goes. Also clean where the air filter attaches to the carb as shown in the photo. Put the air filter back on. Turn the motor over for about 5 seconds or so to suck the stuff into the motor and coat all the parts.
Lets say that again.
You never want ANY small dirt particles to get inside your engine. Never run your engine without the air filter. And when removing the filter for cleaning, make certain that particles don't fall into the exposed carb. It just takes one particle to ruin the piston and sleeve. If the glow plug is removed, it leaves a huge hole that leads straight to the piston and sleeve.