How do I adjust the flapper on the Fluidmaster 400AK Complete Toilet Tank Repair Kit For 1.6 GPF?

Sounds like the float is not attached...it should be attached to the flapper ....it may need adjusting

Hello- If you replaced old ball and rod set with new fluidmasters they will most likely need to be adjusted, not all toilet tanks are of equal height. You will have to adjust water height,meaning you must keep water level below fill tube located in center of the toilet tank. Adjustment is done from bottom of the fluidmaster, they screw in and out to adjust height. You will notice threads along the bottom part of the fluid master, on the inside of the tank,they adjust up & down! Goodluck!

I would put in a FluidMaster system.

http://www.fluidmaster.com/index.asp?bhcp=1

probably needs a "doughnut" tank washer under tank..or try tightening the tank bolt..fluid master comes with a little rubber hose that goes to overflow tube

The Kohler Cimarron is one of the most popular and reliable toilets out there. (My Favorite). However, depending on the hardness of the water and if you use cleaner tabs in the tank, these factors can lead to a malfunction.
The first thing you should do is hold the flapper (rubber seal inside the tank that releases the water down to the bowl) down with your hands for a few seconds after a flush and see if the toilet stops running. Sometimes the flapper doesn't seal properly therefore the fill valve keeps working non stop. Stopping the fill while holding the flapper down will confirm that your flapper needs to be changed.
If this doesn't work then try this....
The other common problem with a running toilet is with the fill valve itself. There is an attached float on the fill valve that goes up and down depending on the water level. Once the water level rises, it rises the float, and the float tells the fill valve to stop filling the tank. While the toilet is running (hissing), try raising the float all the way up with your hand and see if it stops. If it stops but not consistently with every attempt, then you will need to change the fill valve. I believe the Fluidmaster 400A is the replacement model.

Have you recently replaced the fill valve and flapper ?If so make sure they are interchagable and can produce close to the same GPF as original hardware.Fluidmaster has a tall tube that can be cut according to tank depth to accomidate water volume in tanksome times a little more water volume will do the trick.Also make sure flapper is staying open long enough to produce the required results.

1.The Flapper Valve isn't seating all the way, and allowing water to seep through. (At end of chain)
2.The Fluidmaster water control unit that is connected to the other end of the chain, isn't shutting off when the lever for it, is all the way in the down position.

Test the FluidMaster unit, by lightly applying pressure in a down motion, to that lever.
(Facing the toilet from the front, the FluidMaster water control unit is in the left corner of the tank. {Not trying to insult your intelligence}
The lever I speak of, is the small arm at the top of the FluidMaster. The Flapper Valve chain connects to this lever)

If it shuts off, you may have some fine sand, or other foreign material in the FluidMaster. [Taking one apart, and checking, then reassembling, is No fun!]

If it doesn't shut off when you apply pressure to that lever, you may have a bad diaphragm in the FluidMaster.
Suggest you replace this unit.

Check the fill tube in your toilet one easy way to see if it's leaking is get food coloring and pour in your tank to color the water this makes it easier to see and squeeze the tube in the tank when it's full if you see the colored water running down the middle of it you have a winner! if not you can look around for it sometimes the plastic under the flapper gets cracked too

First off,If the air vent was clogged the toilet would back up and overflow and when it did flush, it would make a gurgling sound.
secondly the water level in the bowl is not important as long as it covers the opening,The water is only there to keep out sewer gases so they don't enter your home and the shape of the trap will always maintain the proper amount of water needed to prevent this.
The previous water level may have been due to a partial clog that has since been removed.