400 hrs on the bike, started running hot a few weeks back( hot warning light coming on and overflow of coolant). I pulled the thermostat and checked it,seemed to take quite awhile before vernatherm would open so I did and old outboard trick and cut out the vernatherm and put the stat body back in. Noticed it ran hot this afternoon. Coolant is toped off,radiator core clean as can be,is it time to install a water pump? is it a big job?