Ask The Editors: No More Power For Hills
Questions like yours are very difficult to answer from afar as there are simply too many possibilities to consider, many of which can only be diagnosed by in-person investigation. While you didn’t provide any of the necessary information to get too specific (what year, what size ATV), we’re going to go ahead and guess that you have an early 2000s Trail Blazer 250 in our search for a schematic to study.
Here is one for the gearbox of a 2003 Polaris Trail Blazer 250:
As you can see, there are a myriad of transmission parts that could potentially have let go, causing you the issues you describe. Is it still making normal power elsewhere and simply bogging down when you attempt elevation? Is it grinding when you put it into gear?
Remove the clutch cover and start your investigation there. It’s possible that the clutch is slipping but based on the information you provided, we simply can’t say so with any certainty. If it’s indeed an internal transmission component having failed as we suspect, splitting the cases to access the internals is likely your only option. Perhaps start by checking to see if your output shaft gear may have lost some teeth.