Well, after much tinker, research, and more tinker, the bike's now running very well. Starts, idles, revs and pulls smoothly all the way to redline. No stumble, or flat spots, great roll on response at all levels.
Wow. This thing's a ball to ride.
Thanks for all the information, and more importantly for the encouragement to keep working on it.
First of all, my initial issues were mainly caused by crappy original intake tubes, which were brittle & cracked. I blamed the 6-Sigma jet kit. The intake tubes & o-rings were replaced and it really got me somewhere, but still lots of issues, and the indications seemed that it was running too rich . I went down in jet sizes from the 6-Sigma kit, and generally it got worse; & since it loved the choke when it balked, I then started working my way back up in jet sizes, finding improvement each time. I lost track of how many times I had the carbs off, and how many sets of jets I got, but I think I tried at least 4 or 5 different combinations. Along the way was lots of learning (I can pull the carbs off in 20 minutes now, change jets and re-install them in less than an hour total) and some sloppy or careless work on my behalf. Never underestimate the value of attention to detail at every step.
One issue I had, I blamed on carbs and it was the plugs. Now there's one step hotter plugs, and new NGK plug caps, which made a surprising difference.
The starving issue noted on my last post was, well ... low on gas. Duh. I made the mistake of trusting the very vague gas gauge, which showed a 1/4 tank & I'd just put a gallon in it. (I had never ridden this thing before I started working on it - it's my daughter's bike, she picked it up in neglected condition. I had originally started it on the stand, then commenced all this work, not really knowing what sort of baseline I was dealing with). So, dumbassness at play. "Genius has its limits, but ignorance knows no bounds".
Anyway, for the sake of conclusion, and for the "pods and exhaust" topic, here's the final score:
(SitStat: '82 gs650 gl, 17K miles, 140psi +/-compression; K & N dual pods, drilled out stock exhaust; & sea level riding for the most part)
Pilot jets are up one size (45). Mixture screw 2.5 turns out. Floats set, & rechecked (first time they were off, and it was just sloppy work on my end - a digital mike makes all the difference).
The needle now has no spacer above the clip, & a small nylon spacer + one thin steel washer (from 6-Sigma) below the clip. Vacuum slide hole drilled out w/ #40 drill bit. Vacuum slide springs clipped about 3/16ths inch. Main jets are Mikuni's (I doubted the quality of the AB jets supplied in the kit) 127.5 on the outer cylinders, and 130's on the center pair. I also closed/covered about 1/3 of the surface of the K & N dual pods.
Some of these things are a bit contrary to the advice I'd received, but I just kept trying different things following trial and error until it started showing improvement. All bikes are different, and riding conditions vary of course, too.
I kinda hate to turn this thing back over to my daughter now that it's done, it's so much fun to ride.
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