If a toilet's siphon jet does not work, it will affect the toilet's flushing performance by not allowing in sufficient water from the tank after each flush. It's important to act diligently to repair this problem.
Mineral deposits or foreign objects sometimes clog the siphon jet, preventing it from allowing in the normal flow of water to help create a strong siphon action in the trapway. The result is a weak, slow flush. You may find yourself flushing an additional one or even two times each time to empty the bowl, which adds up to a larger water bill and use of natural resources.
Fill a bucket with cold water and dump the entire bucket of water into the toilet bowl at once. If the toilet flushes in the way it should, that proves that when the toilet is ordinarily flushed, the flow of water is not sufficient enough to create a proper flush. You can also test the jet hole by holding your hand in front of the siphon jet and flushing the toilet. Notice if a strong current of water enters through the siphon jet.
Straighten out a wire coat hanger and ream any mineral deposits from the jet hole with the hanger. If a foreign object is blocking the jet hole, it may be necessary to remove the object with tweezers.