Let me set the scene here - I had discovered an apparent overheating problem with my ZZR 250. Recent on-site testing at Racer Replica showed the temp gauge flickered violently, but usually showing just off cold. All of a sudden, coolant spewed out from the expansion tank, with the gauge jumping up to half - plus the flicker. When she cooled down, a coolant levels check showed the radiator at full, and the expansion tank wanting a top-up. The suscpicious cooling system components wer the temp-gauge sender, the thermostat, and the head gasket. Well, when I removed the fuel tank and accessed the thermostat housing, I discovered a loose connector on the sender. Tapping the head of the connector tightened that up, and the temp gauge now speaks the truth. Without a thermometer, I tested the thermostat on the stove in boiling water. It took a heavily-bubbling boil for it to open, and then it only opened a little. Keeping the thermostat out, I have since reassembed the bike, filled and air-bled the coolant, and took it out for a putt. At speed, temperature leveled off just below 1/4. Hanging around a servo a while showed the temperature climbing up to half, then the thermofan kicked in to bring it down. That's much more like it, and it looks like I can rule out a bad head gasket. Now to pick everyone's brains. I have ordered a new thermostat, at factory spec to open 85-90deg. Meanwhile, apart from taking a little longer to warm up, does anyone know of any issues in running this carburettored ZZR without a thermostat for a while?