What flywheel are you using?? The brass collet (thing under the flywheel) on the stock flywheels has a habit of getting deformed if you take the flywheel off and put it back on. If you turn your engine over slowly, and have this problem, what you will notice is that flex cable collet will woble (not stay in the same spot). If this is what is happening, you might want to try a different flywheel. The SV27 one works pretty good, but only has a hole drilled in one side of it. A guy at a hobby shop showed me that the flywheel is not balanced like that. So, I drill the hole all the way through and it balances it out better. Other than that, there is an OS blue flywheel, but if you are belt starting, this one does not work very well, and may actually rub on the bottom of the hull in a stock MV (not sure about the deuce).
Another cause of the cable breaking here is soldering. I got too much solder into one of the cables when I soldered it prior to cutting. This made the cable brittle. Could not see it from the outside until the cable broke, then I could see that the solder had wicked down outside the collet.
Sean