My bike was doing a similar thing last year where when the fan came on it would start to sputter and break up, bring up the rpms and it's fine. I didn't really mess with it until this spring when I found a bad fuel pump and since replacing the fuel pump the problem hasn't happened. I think it may have been because the bad fuel pump was drawing so much and then after a certain rpm the fuel pump turns off and the bike is pulling gas for itself. That would allow the fans and ignition to run fine after you bring up the rpms. I don't know if my reasoning is accurate, but I haven't since had the problem.