Runs great, but stalls out under power

[Catfish]

holy moley

I believe I have solved the mystery. I started taking the exhaust apart beginning at the block. All seemed well with no scale or soot buildup, although the old exhaust hose definitely needs replacing. I looked into it and couldn't find any signs of collapse or obstruction. When I got to a check valve in the system I found an old corroded check valve with the flap pin completely disintegrated and the flap rattling around inside. I opened it up and removed the flapper, essentially making myself a coupling. ABRA KADABRA....engine is running fine against the dock lines for the last ten minutes at about 1/4 throttle. Could that restriction be causing back pressure and causing the sooty plugs??? Going for a test run in a few hours when it cools down.

[Dave Neptune]

Bingo for blocked exhaust!! Now that would be a blockage.

Take a look at the plugs after running, may be just fine.

Dave Neptune

[roadnsky]

I PULLED 2 AND 3, THINKING IF THE ENGINE RAN BETTER IT COULD BE EXHAUST BLOCKAGE.

Exhaust... Bingo!
So glad you've found this. (Feels good 'eh?)

I guess some of us wrote off the exhaust blockage too easily. (me)
Sorry. It seems so obvious now.

Cat-
This is one reason you got so many questions even tho you had (in theory) crossed off that issue on your checklist.
It is the hardest part of contributing on this forum...
Troubleshooting remotely without the benefit of the senses of seeing, smelling and touching.
AND... the keystone of this forum...
Being reluctant to offend or "flame" someone in expressing an opinion.

So... celebrate your troubleshooting and DYI skills! Congrats!

[Catfish]

Thank you Jerry. It does feels great. I was at wits end and had started researching electric engine conversions lol. Thank you EVERYONE for your contributions to this thread. I've always been a cheerleader for the A4. I hope I can give back to this forum as much as I've taken. If any of you are ever in the gulf beaches area of St Petersburg Florida please accept my invite for coffee or a cocktail.

[Surcouf]

not the first time on this forum: air, fuel, spark.... and an open exhaust!
Well done!

[ndutton]

Something to consider

I just made this post on another thread and it brought your resolution to mind:

My set-up has been trouble free for the 16 years I've owned her but I would not offer it as an example to follow. My boat is a Catalina 30 and by its mid-cabin engine placement and surrounding cabinetry, it is one of the more challenging boats in terms of exhaust system design. Over a 30+ year production run with more than 7000 C30's produced, even Catalina was constantly modifying the exhaust system design with mid run check valves, outlet flappers and ever increasing waterlift volume.

Every party has a pooper so in that vein I bring this question: In removing rather than replacing the check valve you have eliminated an exhaust system component that Catalina thought was important enough to install. I'm not suggesting I have some mystical knowledge that it is absolutely necessary, more than a few C30 owners on this forum have done the same without any reported issues but still, Catalina thought it was necessary and now you no longer have it. Even before removal it probably wasn't operating properly for quite some time.

If memory serves, Catalina stopped installing the check valve at the same time as they made other exhaust changes like the external flapper and the jumbo waterlift. Did one predicate the other? I dunno but the question is, are you confident the check valve is not a benefit in your particular exhaust setup? When my check valve failed (they all do sooner or later due to the steel hinge pin) I didn't feel strongly it was necessary but Catalina did so I deferred to their design considerations and replaced it with an all stainless valve.

[Catfish]

Neil - Thanks. Definitely something for me to consider. For this week I'm motoring about five miles on the intercoastal to the boat's new berth without it. I'm going to get a replacement on order tomorrow, as well as a new through hull and exhaust hose. My hot section and mixer are fairly new and in good shape.

[ndutton]

I'll repeat for emphasis, I'm not saying I think the valve is needed but neither am I saying it's not. Catalina felt it was. When I sourced my replacement stainless valve (McMaster-Carr) I confirmed the flapper hinge pin was stainless too.

Good luck on your relocation.