If this kind of situation didn't get worse, then nevermind. Hope that everyone could really votes and comments fairly.
Remove it from the GRS system - kinda pointless since you've done a great job in making it
Have some sort of pop-up when you vote explaining how to vote - for example explaining that a 9 or 10 should be given for the best chops in this sub-forum (those deserving promotion) and not necessarily the best chops on Autemo (and make it so it's not so intrusive e.g. a "Don't show this again" check-box if you already know how to vote)
Weight the votes on forums accordingly - for example take a sample of a fair number of chops from each sub-forum and average the score given to each chop. If you wanted a voting system so that the ratings in each forum are consistent (i.e. an excellent chop in Elite is given a 9 and an excellent chop in New Choppers is also given a 9) then you could take the average score given to New Choppers (let's say 6.5) divide it by the average score for Elite artists (say 9, which = 0.722) and then divide the score for what the New Chopper got on their chop (let's say 6) by this "weighting" to calculate a weighted score, so 6รท0.722 = 8.31. One benefit of this is that it would require no changes to the way people vote and wouldn't bother anyone. It would be best if the forum didn't show the weighted average otherwise people might get a little confused, but it could be used as a direct input into the GRS points system to make it fair.