I have tried several different times to burp my cooling system. I have an 08 Vulcan 900 w/140,000 mi on it. I keep getting back pressure in my reservoir which pushes out coolant and causes bike to overheat. Can't go over 70 mph or the coolant gets the back pressure too, which pushes out the coolant from the reservoir cap/overflow. I have taken off the cap and ran until fan kicks in, waited for it to cool then filled tank to top. I have even elevated front wheel, did the same process, still gets air bubble. I have given it throttle at high rev until fan turns on, cooled it, then refilled it and still gets back pressure within 400 miles. Depending on traffic or if I drive 70 mph continuous. I have squeezed the bottem and top hoses prior to topping off, then even after, before replacing the cap. Cap, thermostat and all hoses have been replaced. What could I be doing wrong?