Try to be more specific. Analyse your traffic to see the words that are being used to find you. Broad match is exactly that, broad.
If your adverts include the first 4 letters of your username then you may be surprised to hear that Google may deem the manufacturer on its own to be close enough to be a broad match!
You can check this by doing a synonym check:
~keyword
Any highlighted words in the results are synonyms according to Google.
Go through the searches that have been used to find your site and start creating a list of negative keywords such as any other products that the manufacturer makes (possibly with more wheels ;). Whilst doing this you should try to identify the terms that are specific to the subject in question, adding phrases that make sense with those keywords in may help.
A good list of 2 or 3 word phrases on broad match with a nice set of negative keywords may make a huge difference.
Bidding on single words (if you do) is a recipe for disaster.
Good luck.
