Just signed on and read this. Have had FZR1000RU for ~4yrs am on 2nd engine - last one dropped a valve at around 80K miles. It ran within temp limits (just) within town. Changed engine ~1.5k miles ago (6weeks) it ran hot and would ´boil over´ if stationary for any time even though the temp guage was not in the red. Checked & cleaned radiator - all ok. No gases in rad whilst running implying no head gasket problems. Timing was fine so problem pointed to radiator cap. Like the ones for many (English?) cars it has a spring to seal the rad from the overflow tank, the spring presses on a washer which has a rubber seal next to it. The seal presses on the neck of the radiator filler. Once pressure exceeds 15-20lb/sqin, pressure lifts spring, and removes the rubber seal from the top of the rad allowing the coolant to exit along the overflow pipe. If too much exits (it always does) then the tank overflows. With age/use the rubber seal on the cap degrades. A new rad cap costs £30. Standard Jap bike over-pricing. I Bought an O ring seal that filts into the top of the rad so now the seal on the cap mates against it rather than straight onto the metal of the radiator filler. It cost £0.15 and works a treat.