CO Meters are expensive and hard to come by.  In the early eighties, I =
had two 911s in California and always had trouble with shops incorrectly =
setting the idle CO.  To correct this I looked into buying a meter (big =
bucks).  However a friend directed me to the local Heathkit (Zenith) =
dealer who had a CO meter that you could build.  Yes, it takes a couple =
of hours but I still have it and it.  It has always checked out against =
all smog tests in CA and Utah where I now live.  It cost about $150.00 =
but it is still a wise investment for EFI or Carbs (I use it to dial in =
my Webers on my 2 Liter Type IIs)

Hope this helps