I have a 2000 Honda 400ex and there is gas in the oil. Does any one no what may be causeing this problem. Thank You

 

Your carb is leaking, and its going into the motor, and washing down the cylinder. At a minimum, you need to turn the gas valve on the tank, to off whenever the motor isnt running.
Then youll need to remove the carb, and clean out the float needle and seat, so the flow can stop, once the float bowl is full.

 

The excess gas should go out the carb overflow, so that is most likely plugged or kinked....along with a likely float that is out of adjustment or has some grit under the needle.

 

Also make sure the tank vent isn't obstructed. I had a motorcycle with that problem, and if you parked it in the sun with a hot engine it would dump gas out the aircleaner, the float drain, and down into the intake where it eventually seeps past the rings and into the crankcase.

It would make a "woosh" as pressure released when you took off the gas cap, and immediately stop leaking. I didn't realize a bad vent on a gas tank could push fuel past the carb's needle, but correcting the tank vent solved the problem.

 

Back in my dirt bike days as a kid, we were taught that you turn the gas valve off even if you just stopped to take a break out on the trail. The way they explained it to us, was that if the bike fell over it would flood gas all over the place and then when you tried to start it, there could be a fire.....

Anyway, I have carried that training with me all these years, and am a stickler for turning off my fuel valve. That no doubt has saved me from procircuit's experience several times!

 

Yeah. The bike I had that problem on has a vacuum petcock, that shuts the fuel off when there isn't intake vacuum. I was really surprised that pressure from heat and an unvented gas tank would push through both, but later I learned there was a recall for the same problem with a different model of the same year and make...

It is a good safety practice to shut the petcock off. Also if the machine is going to sit for a while running the float bowl empty will make starting it next time easier. Gas goes stale faster in small quantities exposed to air (like in the float bowl).