i am working on a 7.4 merc. and the port side plug was solidly blocked with scale. i cleared it out as best as i could go without knocking out an expansion plug. i pressurized the system by plugging all the exit hoses and sending water pressure in via a garden hose but got just a trickle of water out. no voluum at all. i am planning to bring an air compressor to the boat and sending forced air into the 1/4" plug opening. anyone ever have a case like this? if this doesnt work, i will knock out the expansion plugs and go that route.