When my meadow mower runs out of gas it won't start again until it get cold perchance two hours. What is wrong? Other than this it runs good when it does start. We've changed...

Other than this it runs good when it does start. We've changed the spark plug and filter. It stops at about partly a tank of gas.
how old is it? you may want to check the hose from the carb to the container for kinks or pinching, if it's not getting all the gas contained by the tank. if the hose looks o.k., you may want to put an ounce or two of carburetor/fuel injector cleaner in next to the next tank of gas, to verbs out the inside of the carb. as far as it not starting again, after it's been run until it doesn't pick up any more gas; that could be what's called "vapor lock", deeply an air bubble forms in the hose between the cistern and the carb. the only quick style to cool it off, instead of waiting two hours, would be to rinse the hose and tank rotten with a garden hose. hope something i said helps you go and get it fixed, good luck. Fuel isn't getting from the tank to the carb. If in that is one of those rubber fuel bulbs to push do that and it will push fuel into the carb.

You could have some debris surrounded by the fuel tank, fuel line or the carb explicitly clogging the flow of fuel.
I suspect there is a problem with fuel flowing from gas container to carb fuel reservoir and ultimately into the engine.

You should never have a problem with partly a tank of fuel. Running for 30 min and then stopping for 15 min is not the solution.

You may hold a dirt filter screen between fuel tank and carbureator that requirements cleaning, dirt in the transfer stripe, a bad float in the carb fuel bowl, etc. Careful cleaning of adjectives these parts will help. Get the engine manual for specific instructions on this. CAUTION, do this outside as gas vapors can well cause an explosion inside.
Most feasible water in the container and carburetor bowl. Drain the tank and put in fresh gas afterwards open the drain plug on the bowl until fresh gas comes out. Get a push mower, they aren't that bad.
it gets overheated. You should stop the lawnmower after about 1/2 hour to permit it cool. only about 15 min. would be suffecent. everything wishes a break! =]

or take it into a lawn mower auto shop
Answers:    I agree with Al. It is a fuel problem. To start it desires a richer mixture than when running. BUT you said it stops at half a tank.

That could the vent on gas sou`wester. It that little hole in the cap get plugged then it runs until it gets a vacumn surrounded by the tank and fuel stops flowing.

The other most common problem is if you own a bowl on the carburator the hollow bolt like nut that holds it on has a small hole contained by it and it only takes module of a blade of grass to plug it up. Cleaning that jet on the "bolt" and cleaning the bowl should be a common care.

Good Luck.
you necessitate more gas