Re: yet another 15hp question

[Don]

Yeah, sounds like the symptoms of a grommet(s). Sometimes, you will start the engine and notice the telltale working, but it slows and sputters as the engine heats up. Then, it will puff a blast of steam right out of the telltate when she really gets to cooking. I’m very confident you will find crushed grommets.
Before you pull the powerhead, try to determine if the upper mounts are worn/shot. You wouldn’t want to miss the opportunity to change bad upper mounts once the powerhead is off.
Good luck with the bolts, there are four more under there that hold the inner exhaust tube/grommets under there as well. Use the torch if they don’t want to budge.