A "skip" ( usually four stroking ) does not necessarily indicate an air leak.

If the engine is rich, it will do this. It may be that you have it too rich.

Check for a leak by:

Put a CLEAN piece of fuel tubing on the carb inlet nipple.

Open the throttle and turn the engine over until you can see the crankshaft opening, permitting you to see into the casing.

BLOW into the tubing. You should hear a HISS and feel pressure being released.

Put your finger over the carb opening to seal it.

Now turn the engine over as you blow through the tubing.

At some point you'll find that the pressure does not seem to go down at all. Hold the engine at this point, and keep blowing ( maintaining pressure ).

If you have a leak the pressure will go down after a few seconds. I doubt it though from your description.