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Contrarian 22-09-2012 21:40

Outboard gagging on carbon monoxide
I have a Haida 26' with a BF8 Honda outboard that sits in a well (vs. hanging off the transom). Runs like a charm at the dock, but under way seawater floods the well, so the exhaust cannot escape out through the bottom (where the motor exits) which causes the motor to suffocate in it's own fumes ... it coughs, sputters, and eventually dies.

I suppose I could install a blower to exhaust the CO but that draws amps, thus not the ideal solution. I've tried drilling a 1-1/2' hole in the outboard cowling (next to the carb intake) with a hose (like a snorkel) to a vent in an attempt to drawl fresh air so it could breathe, but that didn't work either.

Absent installing a diesel, I'm plum out of ideas. Any elegant solutions or creative suggestions?


cal40john 22-09-2012 23:36

Re: Outboard gagging on carbon monoxide
Check the exhaust pipe where the water is injected. Our club has had 3 older Hondas that wouldn't run with the cowl on once the stainless steel exhaust pipe corroded through and let exhaust into the cowl. Some (many) of the Hondas have the exhaust exit through the hub of the propeller, so your problem wouldn't be with the well. Does your prop have a cone on the end or a flared opening in the center?

If it's the exhaust pipe have fun, you have to take off the lower end and the power head to replace the exhaust. You also need a manual to find the last hidden bolt to get it apart. We beat on one of those poor engines quite awhile before someone decided to look at the service manual.


Florida Mike 24-09-2012 07:36

Re: Outboard gagging on carbon monoxide
If the above post doesn’t solve your problem this might help.

Most outboards get their fresh air from the underside. You started with the correct idea next you need to seal up the original air intake. Also make sure there is a safe way to exhaust the fumes out of the motor well. That will most probably be more for problem than the rest of it. You also might seal off closer to the leg of the motor so that the exhaust goes out below the water line and while you’re underway should bubble up behind the boat. Just my two cents, Mike.

Blue Stocking 24-09-2012 08:07

Re: Outboard gagging on carbon monoxide
Once had a Pearson Ariel that did this. Put a cowl vent on the transom and the lazarette hatch top. Solved the problem.

Contrarian 24-09-2012 11:16

Re: Outboard gagging on carbon monoxide
John - I think you might be onto something so I did some research, and yes indeed, this motor does exhaust under water, so the fact that the motor sits in a well most likely has nothing whatsoever to do with it, other than the well limiting it's fresh air - this is likely why all my venting ideas have failed. Therefore (occam's razor - find a hypotheses that which makes the fewest assumptions) exhaust is probably leaking from a corroded pipe into the cowling. I will chase this lead and see where it takes me. Thanks all!

Acushla 24-09-2012 17:13

Re: Outboard gagging on carbon monoxide
These engines exhaust under water during their normal operation. However this requires the exhaust pressure to be greater than the water head above the exhaust port. Therefore you need to ensure that there is no restriction to the exhaust such as either carbon build up at the exhaust outlet from the head and/or the exhaust port at the bottom of the leg or calciferous deposits at the underwater outlet.

Test it by putting the engine under power if necessary with the cowl off taking the boat to its hull speed to see if it is a function of lack of oxygen to the engine inlet or failure to exhaust properly. This should give you more data to work on.


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