Your menu bar is not consistent on every page, which it should be. For example, you have 'Brit Bikes' which for a start you should try to fit the word 'British' in.... but if you then click on the 'british bike' link, that british bike button disappears off the list. The german bike link drops when you are on the german bike page etc etc... I understand your reasons for doing this as the visitor is already on the british bike page, however it is still best practice to keep the button for each page you are on, actually on the page or it just means your links menu jumps all over the place. Hope you understand that.
I can also 100% vouch that your Google adsense will stand a much higher chance of attracting revenue for you if you make the background the same colour (color) as your page background (i.e. yellow)
Also I would advise that you don't have the adsense on BOTH sides of the page. LH side is a winner for sure.. but not both. Run the adverts down the LH side, even off the website page if you like, this will make much better viewing for your biker enthusiasts as well as encourage more hits on the ads from those just 'looking around'.
Although under construction still, check out what I have done with the adsense on this site
http://www.bowsandbuckles.co.uk/. It's placed so it doesn't intrude with the website content itself, but also stands out enough to generate a few clicks and also blends in with the site colours much better.
Otherwise, love the site content itself.. some nice bikes there.