Prior to this, the bike was running phenomenally well.When I engage the starter with the enrichment circuit open, the bike will hit but won't keep running. If I hold the throttle half-open, the bike will semi-run. It sounds like only two of the cylinders are firing though.
I've verified that the fuel pump is working and that there's fuel in the float bowls. I verified that there's a spark at each plug and the gap is set correctly. Last year, I replaced the coils and wires too so I don't think that's the issue. When I pulled the plugs, they didn't look fouled either.
The only thing I haven't checked is the air filter but I don't believe that to be an issue as is was replaced last year. Does anyone have any suggestions of other things to check?