my 1977 410 w/twin 454's needs to be primed (pumped ) 15 times or more when engines ( both ) are cold. They start immediately 8 to 10 hrs after having been run. Experienced marine techs have not found any obvious reason; new rotors distr caps and carbs were kited last fall. No one knows what would allow gas to run back after sitting idle for day or more. Suggestions please. Am planning to instal electric marine fuel pumps no matter.