Landing Gear shock strut alignment for cutting boot cowling extension.

[Nev]

To add another data point - I initially kept a small air outlet in the aft fuselage area by the tailwheel attachment point, to allow air to flow through the cabin (and any water to drain out). However this appeared to be assisting CO to be drawn in at the front around the gear struts. I've since found examples on the internet where having an opening at the aft fuselage can create enough low pressure to draw CO into the cabin. During testing I measured CO with the vent open, and also with it blocked off. CO levels were higher with it open, however I haven't measured with the vent open since I lowered the exhaust pipes.

There's quite a lot of info on the web about certified aircraft resolving similar issues, some of them deliberately vent air into the aft fuselage to create a small positive pressure to help prevent CO ingress. It's an area I might revisit but for now I've booked the air outlet off.

[dramsey]

(LOP doesn't generate sufficient CO).

Some real wisdom there that I find that not everyone knows. LOP is effectively more complete combustion. CO is a product of incomplete combustion (think ROP). If you have CO in the cockpit and cant land immediately, do what it takes to move to LOP and get on the ground. Otherwise you may not make it to your landing spot. And yes even a carbed engine or an engine without an engine analyzer can be run lean of peak. Without instrumentation, I would just lean it til you feel the slight loss of power or slight roughness. Your ROP friends will forgive you for running LOP if it allows you to safely get the plane to a landing spot.