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All this carbon monoxide talk has convinced me. In the the name of safety, I will pull the trigger and install a smoke system. The carbon monoxide and the smoke come from same point. I may have to use the smoke to check for carbon monoxide infiltration in cockpit quite often, but just in the name of safety.

I have been trying to solve this issue on my plane for a while now. I only found out about the CO ingress when I installed the smoke kit.

I bought an electronic CO meter after that and realize they are a good investment. I should have bought one after listening to the Sonex podcast about them in hindsight.

I have taped up the holes in the rear tail post but that seemed to make the readings higher. I have since re opened them. My levels are fine with the cockpit vents open but when closing them CO creaps up to over 30ppm ... I find it actually a bit disturbing I can't seem to solve the issue easily.

I extended my exhaust also and have done a few other bits and bobs but again to no avail.

I use a small digital CO monitor that is designed for use in boat & caravans (travel trailers). From memory it coast about $30 Australian. It is powered by two AA batteries (which seem to last about 2 years). It keeps a running record, so that I can review Max & Min. Has both audio and visual (light) alarm. I haven't put it in my new, yet to fly, Sonex but in my last aircraft I had it located in the passenger foot well, away from vents/drafts, where it should read the highest levels and I can see it (when I don't have a passenger). In about 5 years of use it never alarmed and never recorded levels of any concern.

In regards to placing a monitor at foot level . I would at least get a reading at your face level with both the vents open and closed. I found a rather large difference depending on where the reading was taken. A zero reading at your feet doesn’t help much if you are getting 200 ppm at your mouth. If nothing else you will know what reading you get and. Then you can put it at foot level again if you want

CO is denser than air and will collect/concentrate in the low points (foot wells, etc). So the reasons for placing the detector low down is to give the pilot adequate warning of a developing situation.

It is unlikely but possible that air vents could be a rout for CO entry however it is also likly that the CO would be "mixed" with fresh air giving a low reading on the monitor