I have a 175 (143) in the thirty odd years i have been riding i think it is one of the best bikes i have ridden.
I have taken out all restrictors, lowered gearing that is all, i have the new pilot jet as recommended but dont think there is any reason to put it in yet. I competed in a trial last weekend with very tricky sections, tight turns, up 3ft plus faced banks, she did not miss a beat, buckets of power, and i am 15.5 stone.
If you want a bike that is responsive and does not run away with you when you are on the last lap of a trial and feeling a bit nackerd, i cannot recommend it highly enough.
She has been in Birketts but that was because she was using an excessive amount of oil, there was no mods done. Birketts know there stuff and are great to deal with.
Vinnie