have 85 polaris 400 l/c indy , mag side cylinder runs cool at idle, seams to have vac leak, changed mag side seal and top end gaskets , has good compression both cylinders ,checked cdi ,switched wires , carb flanges new , sprayed cleaner all over to find leak , can hold hand over right carb, no change in engine, left side kills engine, any sugg helpful, am i missing something simple