my stock 79 12A (26K miles) starts and idles good, is usually ok for around town driving, but runs bad whenever I take it on the highway for a while, lacks power, won't rev out, backfires. I suspect the carb. rebuilt about a year ago the front sight glass level runs almost to the top of the glass, the rear runs low around the bottom of the glass, exhaust smells rich. but sometimes it runs real good, so I don't know, I'm reluctant to mess with the floats. I've already done the fuel tank, oem pump, new filter, so fuel delivery is good, points, plugs, timing, wires, vac hoses all good. should I open up the carb again and adjust the floats? what else can I check?

 

Problem is your floats. Should be right in the middle of the sight glass. If u replaced your float valves with the ones that came in your rebuild kit. That's your problem. Well know for never working like they should. No matter how long you mess with it. Atkins Rotary sell good replacement needle valves.

 

needle valves and seat are original to the carb

 

In my very amateur opinion I think it is improper float adjustment. I actually finished rebuilding a carb today. I used original needles and seats too. I spent about 30 minutes getting the floats right, when I was done they were spot on to what is spec and nearly exact on each side. Here are the specs I used from the Haynes manual.

And the Haynes photo.