Motorcycle Repair: 1979 Kawasaki KE250 will not say running, kawasaki ke, air screws

Question
I have a 1979 Kawasaki KE 250 (2 stroke) that I have not started in 17 years.  My son and I are trying to get it started.  We cleaned the gas tank, carb and air filter.  Replaced the battery and cleaned the plug.  After a lot of sweat, we started it and drove it for several minutes and it seemed to be running good.  After that short run, it now only starts for several seconds and then dies.  We cannot get it to stay running.  If you turn the throttle it only dies sooner.  Any suggestions?  We tried adjusting the idle and air screws, but no luck.

Thanks

Answer
Pat,
 This could be any host of things however I have the strong suspision you are starving for fuel due to internal carburator blockage.  I know you cleaned the tank and carb. however it only takes one small peice of debris to make it's way down to the carb and foul the needle valve or main jet.  My suggestion; dismantle the carb again, clean, adjust and reinstall.  At this time you must also puchase from a bike shop, a small inline fuel filter to install on the fuel hose leading from the petcock to the carb.  This will trap any loose rust or debris from making it's way to the carb.  Unless the tank was prepped correctly before storage your likely to have quite a bit of rust inside.  There is a product to coat the inside of your tank and seal over the rust (two-part epoxy) you can get at a good bike shop.  This is the best thing you can do aside from obtaining another rust free tank.  If you are not extremly familiar w/ cleaning and adjusting carburators I'll give you the basic rundown:
Disassemble, clean all jets and orifaces with solvent and COMPRESSED AIR ONLY, use NO wire or picks to clean holes/airways. Rebuild carbs with new gaskets and make sure your floats are set correctly. . Do not overlook the float level, be very sure you are not starving for fuel or allowing too much to enter, the spec will be in a good aftermarket manual, Haynes or Clymer.  Bend the tab at the center of the floats to adjust. Inspect the needle valve for smooth operaration and any wear and debris, be sure it is not getting stuck in the closed position stopping fuel from entering. In relation make sure fuel flow is unobstructed and use a good in-line fuel filter from the tank to the carb. Even tiny particles in the fuel can get logged in critical areas and cause havoc.  Air to fuel ratio screw is typically set at 1 and 1/2 turns out from seated. After all is said and done, reassemble, turn on fuel and run. Finally set the idle screw. Be sure your reed valves are plyable, not stuck shut and not cracked.

Hope this helps, give a letter back if you run into problems.

Mike