Wilsons Sandbox

Today I looked at an '88 nx650 with the bodywork removed. The bike shows 12500 mles on the odo.and it appears to be original miles. Bodywork is in good shape with only a few scratches. Wheels straight with no dings, lights intact, overall in good shape. The carb is off along with the tank. The current owner (who is the second owner according to the title) says bike was running fine untill about 5 months ago. Says he ran it out of gas, re-filled tank and bike started and ran fine for a while and then bk-fired, died, and would not start. He started troubleshooting and disassembled the bike to its current state then lost interest. He wants to sale it "as-is". So ....what do you folks think? I like the bike and they are rare in the States but I wonder about internal damage (cracked piston, jumped timing chain, etc.) I have little experince with the big singles but some experience with the 4cyl streetbikes. I have ridden both the KLR650 and the DR650. How does the NX compare to the big KLR and DR? How tough is the NX motor? Common problems? I believe the motor/trans. is basically same as XR650. Any ideas on what the problem might be (the owner says the spark plug has spark and he thought the backfire my have damaged the carb internals)? Many thanks for your input.