On New Years Eve I worked on the Montesa Cota 247 reed valve engine that I have had sitting around forever. Before Christmas, I tried getting spark and fuel to it and discovered that I would get a loud backfire every time I tried to start it. The timing looked right and the points were set properly. I decided to pop the flywheel/mag off to see what the trouble was. It appears that the key was sheared and this allowed the mag to slip. It also appears that this happened a while ago; signs of all the rust on the area where the mag should have been seated. Yesterday, I cleaned out the remnants of the key and made a new key. I also lapped the shaft and mag to try and get things seated properly. Apparently this was a common problem on these bikes with shearing the key. I got everything back together and was able to get the 247 to pop over a few times. Now I think I need to double check timing and then figure out carb and exhaust sealing to insure to air leaks. The compression is strong on the motor so I believe this engine may have sat after the previous owner couldn't get it to run. Good for me, as I can get things set right and get back to riding it.