ive only run my nt16 on 16% so far as i remember. i have read that most engines seem to like an extra head shim if 30% fuel is going thru it, so it might be an idea to have one just to be on the safe side. but to be honest, with the right plug (maybe an os#8?), i would just fill her up and give it a run.

for what its worth, i ran the os18 on both the 16% and 25% fuels (no re break in in between) without changing any shims etc, and it ran fine with a fair bit more poke on the 25%.

while we are on with the nt16 - anyone know offhand where in the uk i can get a piston and sleeve? the 16 or 18 kit, i dont mind which.