My 24 year old VT500 has sufferred a sudden loss of power, is overheating and misfiring. I cleaned carbs, changed radiator, cleaned fuel filters & pipes, checked each cylinder´s spark plug and fitted new spark plugs and now it will only start and run for 20 seconds or so before stopping. The front 2 cylinders are cold after start up, although the back 2 seem to be ok. Could all the problems be caused by the front 2 not firing? What can be done? Any body had a similar experience or can suggest a way to over come problems? Cheers.