I have a 62 mercury comet 170 I6. Drove fine after purchase for a few weeks. Did about 200 trouble free miles. Suddenly car started starving for fuel after driving at a consistent speed. Promptly got worse and worse until it would only idle, and the fuel filter sporadically bubbles empty, then refills, and repeat. Replaced fuel pump (twice), no change. Replaced rubber lines, no change. Replaced entire fuel line from pump to tank, no change. Replaced sending unit, no change. Everything from the tank to the carb is brand new. It usually runs fine for a few minutes but bubbles are visible upon startup and get significantly worse after a few minutes. Ive checked every connection, replaced every clamp, and do not know where else to turn. Always starts fine and idles fine even after running a long time on a hot day so i dont particularly suspect vapor lock. I have a video but i cannot attach it. Thanks guys!