I am a transportation designer by profession. So basically I sketch for a living.
While your title says 'Design a motocycle', it only includes the most vaguest of the details, such as dimensions and weight. There is no styling part of it.
You have to decide the type of the bike first: Superbike, Supersports, Naked, Cruiser, City Riding, Motocross, Cross Country.
Once you make this choice, then we can go ahead with the styling part of it. This is where I can help you. I can pen sketch some proposals for you, once you choose a few, I will start sketching out details, and then based on fresh choices, I can make some photoshop renders.
Since I am a designer and not an engineer, I wont be able to help you with the motorcycle modelling. But will provide highly detailed sketches and renders.
We can have meets every 2-3 days to show you the progress.