After flushing my Kohler 3386 Rialto Toilet the top of the valve assembly shoots water out while refilling the tank wich hits the tank top and leaks down the front. What do I need to do to fix this? Parts?

Yes,there it is!You can adjust your water level at the flush valve..You can see the ball there you need to adjust that so that the water level of your tank goes to your desired level.

Check and make sure the valve on the wall under the tank is fully open, and that the float is not getting hung up on the inside of the tank

There is a screen @ the inlet to the vavle where the water connects that may be plugged or contact Kohler they will send you a repair kit for the fill valve.

try turning the fill valve down

Take lid off and check that the fill tube is in place. If so flush with lid off to see were the water is squirting from, be prepared to clean up water...If you can, do a slight flush. If there is water coming from any where but the bottom of fill valve and the fill tube you may need to replace the fill valve. In my experience, the fill tube is dissconected.

For Diagram
http://www.askmehelpdesk.com/attachments/plumbing/19906d1242687133-shut-off-valve-under-toilet-doesnt-work-fluidmaster-20ballcock.gif

First things first, remove the fill valve, and the flush handle mechanism. This will give you plenty of room to work with the flush valve. Before installing flush valve lubricate tabs with plumbers grease. Now put on a pair of work gloves, pushed down very hard and turn the tabs should slide easy because of the grease. Remember do not alter the gasket, the gasket needs to be compressed to do its job. I know removing the fill valve and the flush handle seems like a pain, but there is no way to get your hands in the proper position to install the flush valve assembly.

Check the fill line in the tank and make sure it is connected from fill valve to overflow tube. After you flush the toilet it fill's the bowl and tank.

It should be a line about 1/4 ' in size coming from fill valve to overflow tube.

check water level in tank if low adjust float to proper level inside tank will see a level line also check flap as to opening all the way may have to adjust chain if problem continues hard water can cause build up in water holes and narrow tank to bowl tube

you unfortunately need a new fill valve. I say unfortunately because they are expensive, (about $120), for that model and not everywhere sells them. It it was a "regular" toilet, the part would be a any home store and cost about $10. Sorry to be the bearer of bad news. How old is the toilet? You may consider replacing the whole thing.

You need to replace the flapper and you will need to purchase one specifically for the Kohler toilet. I have the same toilet and tried using a generic flapper and from experiance, it didn't work until I bought the correct one and I'm a plumber! Have a great night.