the smallest i have run on 0% is a .18 it runs well, i also have a .32 that runs well. i see no reason why a .25 would not work on 0%. magnum/asp engines love 0% nitro and tons of castor espically when new....if your mixing your own fuel mix 1/6 of it castor (16.6%) 1-2% synthetic to keep the gumming to a minimum and you asp/mangum/wallet will love you for it (costs about 7 bucks a gallon)