What about compression, it might just be that time to rebuild your motor, new piston or sleeve perhaps. How long or how much have you run in that motor, it might just be coincedence that it happened when you switched fuel.

Having said that, motors dont just quit one day, they gradually loose performance and would start giving you problems, starting, tuning etc. etc.

Also if you changed nitro content (%), it is suggested you also change the type of glow plug (hotter, colder), proper shimming is also recemended.