Your engine will run fine without nitro, however it won't idle well. Use a hotter plug than normal and you might be ok. Same principle applies to two strokes. With the extra stroke and no ignition the 4 strokes cool off a lot faster, so they need to be kept warm if less nitro is used. Ideally, in the long run if you plan to do this for a long time get an onboard ignition system. (about 70 bucks)
Max

I run 5% nitro 18% oil (20/80 castor/synth) in my OS FS-52S.

I tried 0% nitro, and it worked well, but it was harder to adjust the idle mixture. But it was fine for sport flying. The fuel consumption is very low, but there is slightly less power than with 15% fuel. By going up to 5% nitro it idles smoother. I have settled on 5% because it runs smoothly but still costs a lot less than 15% here in Norway.

"I have heard" that OS engines are made for higher nitro than Laser engines. OS recommends 5-15% nitro for the FS-52S. To compensate for lower nitro, Laser engines have higher compression. My Irvine .53 MkIII runs perfectly on straight fuel, and it has a very high compression. So I guess it all depends on what fuel the engine was made for.

Tore S