Andersons Baby Spitfire

Gi'day..ill get quickly to the point.i have an early baby spitfire (it came with a red spinner an alloy nose peice) ive fitted it to a few Freeflight models of varing sizes and it dosent seem to be able to "pull theskin of a tub of cream" in outher words its gutless.im wondering if thetre is any thing im doing wrong?? im useing just 10% nitro an plain caster (20%) i found the NVA is in two peices but im guessing its normal ...i aslo need/lookin for anouther NVA as one side of the needle side of nva is broken and sucks air even with silocone tube over it.so iv any one can see what im doing wrong ...im all ears ... fanks for listening....gazza :-)