Seems to me that you should have the hose design, as mentioned above, by retiredoz, if yours is really an ’84 4.5. Sometimes people base what they have on what others have told them; and with Mercurys especially, that seems to be wrong, too often. Anyway, the red nozzle from a can of WD 40 or the like is a great thing to keep handy. They clear clogged Merc telltales out, nicely. If that doesn’t work, with the engine not running, blow back through the outlet with compressed air; then try running it again. If you see steam or exhaust gas coming out of the tell tale hole, stop the motor because you have a serious problem.

I’m asking at the risk of laughter. What is a "Tell-Tale"? George 4TSQ