So I went out to ride twice yesterday, the first time in the morning the bike ran fine. The second time it was a mess. The idle was hunting/surging and there was a knock from the motor just off idle when giving the bike a few revs. It was also surging badly when riding at small throttle openings, i.e. just rolling at a steady speed down the trail.

Any suggestions on where to start looking? It's a '13 Evo 300.

Edited October 11, 201411 yr by heffergm

Sounds like blocked pilot jet. It could be as simple as a drop or two of water in the float bowl. If I was you I would strip the carb and clean it out, blow through all the jets and passages and make sure all is spotlessly clean.