I have an AC 650, I took the air filter out to clean it and noticed that the screen under the element had a couple of marks on it that look like burns right above the carb to the rear. Is this a sign that the valves need adjusted? Or am I possibly running to rich of a mixture? I have no clue when it comes to these motors so any input will help.

 

We've seen it on everyone we've ever worked on I think its from backfiring myself but not 100% sure, If you quad is an 04' it might not be a bad idea to get the valves checked but I don't think the black marks are a sign of valves being out of adjustment.