Yes, I did buy it this way, and the previous owner put the mac pipe on it, and goofed around with the carb, and even tried another carb from an 86, then put it back on and sold it to me as his wife just decided to buy a newer and larger bike. So, I really do not have a "starting point". I do understand your thinking as you really have to change only one thing at a time to be certain what changes are causing what results.
Yes, I checked the float vent tubes with petcock on PRI. I also pulled the carb out and verifed the float needle and seat are sealing good and working properly with the bowl off and the gas hooked up. Not sure about the level, but it is not flooding out the carb and I do not believe the float is low as the bike idles good with a bit of choke on, and the choke is drawing fuel from the float bowl also. Also when I remove the carb from the bike, a decent amount of fuel is in it.
Idle mixture screw was pretty well stripped when I got the bike
Looked in and saw two small triangles instead of a flat slot, hence why I asked what kind of bit it took, as I was hoping it was a special bit instead of being a badly stripped flat head. I tried to remove it with no luck, as it gets to a point where it just spins and spins and does not come out of the bore enough to grab it with anything. I can manage to adjust it though, just takes a little patience and a nicely sharpened flat head.
I picked up a 55 pilot jet (the only one they had in stock) and may give that a shot tonight. I'll let you know if I find the time to try it out. I do have the 1/3rd spacer in there right now also, and I do not see the decel backfires anymore (which it did bad with the stock white spacer in the carb). Also to note, the previous owner told me he took the white spacer out, yet it was in there when I opened it up. They also told me they had tried another carb (from an 86) and had raw fuel leakage at idle once and promtly switched the carb back to the 87 stock one, they probably tried the 86 carb without any white spacer explaining the fuel leakage they experienced and I have read about on here.
So, I hope I answered all the questions you asked, and probably a few that you didn't. Thank you very much for your assistance, it is greatly appreciated. Joe