Like I said before not on a Dyno b/c it's like running on a treadmill. It doesn't account for wieght and stride of a runner just like a Dyno doesn't account for wieght and acceleration of the bike. Power is the ability to do work, the ability to do work comes from wieght loss and higher revs per minute. Air fuel mixture has a lot to do with that b/c it accounts for the revs. Sprockets and a stronger drive chain help as well, keeping the power to the rear wheel.
In summary Horsepower doesn't matter anyway, b/c if you take a liter bike or a 600 to a quarter mile track you are wasting your time. Take it to a real track and see how you do, after a few lowsides maybe you'll understand horsepower to the rear wheel isnt always a good thing in the corners.
Like others have said...decreasing weight absolutely will not increase horsepower. Horsepower is a function of torque. Horsepower numbers on a dyno are not even measured. A dyno measures torque and then calculates what the horsepower is by doing the formula of (torque(ft-lb) x engine speed(rpms)) divided by 5250=horsepower.
This is why the torque figure and horsepower figure are exactly equal at 5250rpm. This is true for any and all motors...cars, bikes, semi-trucks.
By decreasing weight, all you do is create a better power to weight ratio. Which is what will win you a drag race! A 150hp motor in a 1700lb Harley will be slower than 150hp motor in a scooter. The same motor will produce the same power...it just has less weight to thrust.
Also, a bike or vehicles weight is completely irrelevant on a dyno. As far as the dyno is concerned the vehicle is weightless. The "treadmill" that it is running on is a specific weight...often time 550 lbs. Being that 1 hp is defined as moving 550 lbs a distance of 1 foot in 1 minute. By having a roller with a known weight, the computer can do its calculations to determine torque and hp figures.
That is why dyno runs are usually done in a high gear. The test needs to be done over a period of time. So that way you will know the weight of the object being moved (roller), the time of the pull (30 seconds or whatever) and the distance the object is being moved (the circumferance of the dyno roller).
I know this thread is ssuuuppppeeerrr old but I hate people getting incorrect information.