[bobcowan]

Over 10 years ago (last time I had a carb) the same thing happened to me. Sudden and dramatic change. I went through the entire ignition system - twice.

Then I took the carb apart. I found a piece of debris stuck in one of the main jets. Removed that, put the bowl back on, and it ran fine again.

As to where the fuel filter is, it could be almost anywhere. It should be as close to the carb as possible, though.