Try removing the headshims under the cylinder head to increase the compression ratio, it may help with general performance with lower nitro.

It is "normal" for four stroke engines to require some nitro, specially for idle.

My thunder Tiger 75 4 stroke didn´t like 0% nitro fuel at all...couldn´t get more than 8300rpm...with 10% nitro it goes to 10640 rpm.

Bigger engines tend to work better with lower nitro than smaller ones though...