i just had a similar problem. my bike had been standing for about a couple of months, and i thought it was fuel related, i.e. stale, blocked or icing. the bike had only done about a thousand miles since a major service, so i just assumed plugs and filters were ok. anyway, i took the plugs out and found the front plug to be covered in carbon. the haynes manual suggested either the fuel mixture or the air filter. it turned out to be the air filter. clogged up over one side of the carby. quick clean of the plug, new air filter and she's back to normal.
after reading the thread here on k&n air filters, i decided to go for one. i too went to work on my airbox with a cordless drill.
