I tune alot of customer carburetors, and I just needed a simple rich/lean AFM type meter, but, customers usually don't want me inserting a bung in their exhaust (or its falling apart). I found this cheap meter, from Gunson, the company that Makes Colortune, that I have been using for years. $300 as of last month (april 25).
I hooked it up to Ralph, my white 81 250 unadjustable carb 6. After simple calibration in air, 2%CO, Ralph's exhaust was 4.9% Supposedly, 5% is perfect. When running it up to higher revs, it went to 6% (richer) So, Cool. Damn carb seems to be set up reasonably well. huh.
The idle rich/lean screw points towards the cylinder head and requires a special too to turn it, way down low. Easier to remove carb and turn it, and reinstall it. Its a stock varijet II. POS.
Meter works great. Will be using on alot of customer cars, and my Yamaha, which has 4 into 4 exhaust for cylinder by cylinder tuning.. Evil grin.
Someday I will replace the "integral head" with an earlier head, that I have on the damn shelf. Have the Edelbrock carb too.