[Funracer]

I am on my second Gunson Gastester. Accidentally knocked the first one off a stool and it broke, so don’t do that. The GG does, I think, give a somewhat accurate measurement but it says results are +/- .5 which is a lot. Cannot remember what number you are looking for on a 78 but on my 83 the range is .4-.8% CO so a variance of .5 is pretty significant.

Read the instructions several times to get the hang of how to use it. There is also a GG video on YT.

I too have an analog AFR gauge. The GG is much more sensitive. It will display very small changes in the mixture screw that you wont see on the AFR.

Initial setting of the idle screw is easy. Clockwise til closed, then CCW two full turns. That should get you in the neighborhood.

Lots of info here and online about initial mixture setting. Not sure you need that though if your car is already running. Just start it, warm it up then set the mixture with the GG. Assuming everything else is working properly, and with CIS this is a large assumption, you are done!

The GG is not perfect but it does the job and way cheaper than some of the other CO testers. New GG are $250-$300 occasionally one pops up on the forum here for less.