i recently bought a 28 fastfour sedan and shes hard to start.only when i jump her off with twelve volts and she spins over fast will she start then run strong for about 15-20 minutes then stall !i just pulled the tank off and cleaned her out and sealed it with a sealer kit and also blew out the main line!i also took the vacume tank apart cleaned and inspected it then put her back together but she still has the same symptoms!i also took the carb apart and resealed eveything and inspected the float wich was fine!she has plenty of spark at the points also along with new plugs.my next step is to pull off the head and decarbonize everything and replace the head gasket. would that have anything to do with it such as the head gasket unsealing at a certain temp on these old timers??