h8twd

Hi, Iv recently bought a 2006 Sherco 290 after being out of trials for about 5 years. Was out at the weekend and all was good apart from the bike needing setting up for my riding position etc. After trying some hills on it and it feeling a bit underpowered I thought I would take the carb off and give it a clean. When I took the mud guard off the air filter was totally manky black, I surprised the bike even ran. The airbox was full of watery mud and the intake to the carb was full of grime. I also found it had a Keihin carb fitted, which wasn't advertised. Is this due to being a 290? My last one was a 250. Anyway I cleaned it out and unblocked the jets etc. I also adjusted the float level as fuel was constantly coming out the overflow. Now the bike wont start. I have checked the plug and its getting fuel and there is a spark. So iv set the float level back to what it was and still wont start. Could the bike be getting too much fuel now due to being starved of air before, as to be fair the bike ran pretty good considering the state of the airbox. I should also clarify that the mud and water was not off me as was a totally dry day. Hope someone can help. Not sure what to try next? I di wash the bike off so im wondering if its a week spark caused by water getting into electrics? Tom