This weekend I was trying to get the air fuel mixture right in the car, but I couldn't figure it out... I'm not sure why but turning the air bypass screw on the air flow meter doesn't seem to adjust the mixture much at all. I tried using the voltage from the O2 sensor (this is hard because the voltage jumps all over the place even if I get the sensor hot first by revving the engine for awhile.) I then tried using the colortune (clear spark plug that I ordered.) It's pretty cool to see in the cylinder while the engine is running, but it was hard to set the idle mixture using this. I had intended to make a video of this, but blanked... What I noticed is that the engine is stumbling somehow usually combustion appears blue with a hint of orange... which is about what you want (I think). However,  I can tell through the colortune that the engine is stumbling at idle, I'm not sure if it's missing or what but occasionally I get a drop in rev and a bright orange mixture for a single explosion or two. All of this was seen through cylinder 1. I am planning on looking through the other cylinders for comparison, but I had a mixture setting 'fuck it' moment and moved on to other things.

I discovered several small exhaust leaks coming from the exhaust manifold while replacing the O2 sensor, I think they are from cracks and they must be small because they are extremely difficult to locate and disappear almost completely after the engine gets hot. From what I've read I doubt these are the root cause of any of my problems so I'm going to ignore them for the moment.

I checked the temp sensor at low and high temp, seems okay. Checked voltage on the cold start injector, on for 5 seconds then off (seems okay). Used the supposedly unreliable resistance method to check my AFM, and it checked out okay. I fixed my throttle position sensor (TPS) which was not set well and needed to be rotated. This fixed the light puffing backfires on deceleration which I found charming but according to the internet are not an indication of good running.

I also swapped the spark plugs and checked compression. Fortunately the compression tested great between 115 and 120psi in all cylinders. The owner had told me his plugs were recently changed... but he was lying or his mechanic lied to him....

From cylinders 4 to 1 in order left to right. All 4 are different plugs apparently replaced at different times??? Why you wouldn't just replace them all I have no idea, a set of 4 new ones was ~10 bucks. They are all charred black to varying degrees which (I think???) is an indication of rich running, something that my emissions report already indicated. In any case I haven't been able to discern any improvement in the cars running with the new plugs.

I also rechecked the timing (seems okay at idle), and checked that the vacuum advance was working by sucking on it at idle (it is).

I would really like to fix the stumble at idle before I take it back to get my emissions tested again. I think it either has to be a problem with one of the injectors, the distributor or a really friggin sneaky vacuum leak.