I've never used nitro and some time ago someone asked me if a Fox 35 would run with zero nitro. I'd never run a Fox before although somehow I had an old one in my collection so I figured I might as well try it so I could answer him. Fuel was 25% all castor and after I figured the engine felt wet enough to start I gave it a flick and off it went. I stopped it when it was hot, gave another flick and it was running again. This was with an engine so worn it leaked like a seive when put up into compression.