G'day. With low nitro, I'd try an Enya #3 (hot) or #4 (medium to hot). Or equivalents. Enya plugs are very good quality and often work when others don't. My Super Tigre G51 loves a #3 with 10% nitro.

Here in Australia, Enya plugs are freely available on eBay but rarely seen in normal hobby shops which is a pity as they work very well.