[Darren69]

Nice bike! Sadly yes it most likely is the small valve motor as was fitted to standard non S monsters in '98-99. Start by lightening all the spinney bits, clutch and flywheel and then if you want to go deeper primary and crank. Clutch and flywheel are easiest and will give the motor a fair bit more pep and rolling pick up. That's as far as I have gone with my S4 and tbh that's enough for me for now. You'll notice a big improvement that will carry over just as well when you get some proper 900 heads and bigger headers instead of the titchy 750 ones you have now.