1999 Kawasaki KX 125 won't stay running, help!

Just bought a used 1999 KX 125. Cleaned the carb real good and changed the plug. The bike fired right up on the 2nd kick, ran for a few seconds, and then bogged out. I am told that this is what the bike was doing to the previous owner as well. Also, the plug seemed drenched w/ fuel after bogging out. I'm thinking it's running too rich, but I don't know how to adjust the air/fuel mixture. Please, if anybody could help it would be appreciated. Thanks.

Clean or buy a new air filter. Probably dirty.

Check the float level on the carb, could be dumping gas in the cylinder.
While you're at it, find out what the main jet is, and compare it to what the stock one should be...could be way too rich...clean and oiling the filter is good advice too.

The suggestions that the two gentelman made are perfect, I would advise hooking up with someone that has some experience with two strokes and have him/her give you some hands on training. You really need to do a complete check up on the bike, any time you buy a used bike you should do a complete check up and make sure everything is good to go. It can and will save you big bucks and possible injury. Make sure you drain whatever gas was in it when you buoght it and put in new that is mixed correctly and change the oil. By the way how much did you purchase the bike for?

Thanks for all the advise. The previous owner had already drained the fuel before I bought it. A guy at the Kawasaki dealership told me to mix the new fuel @ 40:1, so that's what I did. He told me that originally they called for 36:1, but that was way too much fuel. As far as I know the jets in the carb are stock, everything on the bike is stock. I've got a manual ordered so I'll be able to check the proper float level soon. I bought the bike from a buddy at work. I have ridden it before about six months ago, so I know it's not a lemon... To answer your question, I paid $1500 for it. I'll keep you guys updated on how things come out when I tear back into it this weekend...

That's right! I got it running on Saturday. Man, that was the greatest feeling in the world once that bike kicked over and stayed running. Turns out the carb DOES have an adjustment on it for how much fuel is metered into each stroke. The manual called for bottoming out the screw and then backing it out 1 1/2 turns. The screw was backed out 4 turns! That was it all along. That manual is a great tool... Boy let me tell you what. Thank you all for your help in this matter. I know where to go the next time I've got a problem...

I'll give you an "ATTABOY", and thanks for posting the solution!

Have fun with it