Motorcycle Repair: kawasaki kx 250, kawasaki kx 250, kawasaki kx250

Question
I have a 1997 Kawasaki KX250. This past weekend, as I was riding on a flat dirt road, the bike just died on me. I was riding at full throttle or just under, varying the throttle a little. I was at this pace for maybe about 5 miles. It felt like I either lost ignition or fuel. I checked for spark and have good spark. I checked that there is fuel going to the carb. I pulled the carb apart and made sure there was no dirt or clogged jets or orafaces. The air filter is clean. The exhaust flap and ports are operating properly (there is no excessive carbon build up). The reeds are new and in perfect condition. When I try to kick start it with the air filter off, I can hear what I think  is air being forced back through the reeds and the carb then out through the intake. I don't think that's supposed to happen, but I'm not sure. The most reasonable explanation to me is that there is something wrong with the timing or ignition module. I've got about 100 miles or so on a  rebuilt top end.
Can you help?  

Answer
Hi Jason,

First test is to check compression (pressurize the cylinder & crank). Next would be a leak-down check.

What does the spark plug look like? Describe the color and condition of the plug. Visit www.ngk.com and compare spark plug to those on their chart.

You're right, there should not be any regursion through the reed valves. Reeds should seal tight against compression. Check them per service manual for proper operation.

With so few miles on the top end, I would suspect something related to that repair or prior problem.

Happy Thanksgiving!

Respectfully,
Mark Shively