Misfire on one cylinder

[tkimmick]

Iv'e got a 1975 GL1000, I found that cylinder number 3 is unusually misfiring or there is something I don't understand about it. When adjusting/tuning the carbs, cylinder 3 has no effect on engine idle. When unplugged there is also no change. I have replaced the coils, changed spark plugs, cleaned/tuned the carb, adjusted valve lash, and done a compression test. All cylinders are around the same psi, according to my gauge about 90 but I believe it is inaccurate because im sure it would not run as well as it does that low unless that is the correct number. When I purchased the bike it did have an aftermarket ignition on it, all cylinders do have spark, I've also pulled all the plugs and they all look perfect with the golden brown color to them. The cylinder does not seem to be misfiring according to these tests but it still does not change the idle at all, my question is why? Is this just how the bike is or is there a problem?