Great work Roboknee. I think you've done a bang up job on this biker. Smooth and neat with your colours, good use of spot colours and a really good finish overall. If you wanted to take it to the next level, I would consider adding a bit more contrast to the yellow metal parts - a bit more shade perhaps, to help break up the definition of the model. If you wanted to go one step further than that, a full metal chips on obvious places like the front faring would really add character to what is already a very good model.
You're making great progress with your painting and it's showing through with each new model that you paint. Stick at it and you'll soon have a Waaaaagh to be proud of!