My guess is that either something is rubbing or maybe the reed valves are leaking back a little. I think I hear what you mean by sounding like a horn. It’s kind of squeaky. Given the long history of twos being worn out and/or having bad bearings, I might go with that Idea, too. In the meantime, can you run it without the recoil housing? Maybe start it with a drill motor? That would eliminate that as a problem. While off, pull the flywheel and look for rub marks? Pull the lower unit, put it back in the tank and start briefly to eliminate the lower unit. (Sometimes sound from lower units telegraphs up like you wouldn’t believe.) Then make sure the reed valves are seating well…..maybe even do that first…
Long live American manufacturing!
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