Carbon Monoxide!!!

[sra_tony]

So, I had quite a scare the other day with carbon monoxide in the cabin. Honestly, I don't want to relive the experiance again. But.........

Here I am with a pax cruising down to the Kustatan on an already crummy day. Matter-of-fact I am suprised that I saw other equally arrogant pilots driving other G.A. aircraft both to and from my flight path. (you all know the powerlines from pt. Mac to Beluga) Anyhow, for what seemed like quite a while in hind-sight, I had a feeling of uneasiness for the majority of the flight. Just could'nt put my finger on it. (should have gone home then) but got just over the mouth of the Big Su when it happened.
I started to ask my pax how they were feeling..... I could hardly pronounciate a word! Then it hit me like a ton of bricks I looked down to my cheapo carbon monoxide detector to find it blacker then the inside of a tire. My reaction was first pure terror fortunately quickly followed by instantly throwing open the window and door. I had no idea what to do, so I ended up making some circles right there as I tried to regain some level of comprehension and decision making skills. (wx was crappy, I couldnt decide if to press on into Beluga or 180 back home. nor did I know if the feeling I had would get worse or better) Well to wrap this up and then ask for advice; I should have done several things different. Most noticebly declared an IFE!
I had a mechanic look the bird over and came back with nothing wrong. He felt that for what ever reason, the right A/S and cruise attitude had some how caused a the right kinda cabin pressure to somehow suck in exhaust.
Well this was not the case. Armed with an arsenal of detectors, I officially have a carbon monoxide leak somewhere. It takes only minutes for a "dot" type detector to indicate color change. Needless to say, I grounded till i get this figured out, and am fishing for any ideas, because nothing on my plane seems to be wrong or different then prior to this flight. By the way its a Citabria with a 0-235.

Thanks for any comments and advice.

 

[Morris]

We know it has to come from the exhaust. I would pressure test the exhaust system. With dual exhaust it is easier, remove the valve covers and turn the engine over till one exhaust valve is closed and one is open for one side of the exhaust system. Put an air fitting on the cylinder with the open exhaust valve. Plug the tail pipe with a rubber ball and add a small amount of air pressure 2 to 3 psi. Check for leaks with a soap solution.
With a 4 into 1 exhaust system that has a single tail pipe you will also have to plug the intake before the carb to run the test.
All the aluminum covers around the mufflers will have to be removed to run these tests. While you have them off check all your scat tubes for holes or leaks.
If this tests ok, remove the scat tubes from your cabin heat and block off the intakes with plastic. You do not want any air forward of the firewall to enter the cabin heat system. Run the A/C to see if your detector senses carbon monoxide. You may have to fly it. If you still get indications then you know it is coming through holes / leaks in the boot cowl, belly skin, inspection covers. Tape them off till you find the problem. If you have bad baffle seals this could disrupt the normal air flow under the A/C to keep the exhaust against the belly or coming up along side your side vents.
Good luck