How can I richen the slow speed circuit?

Hi. I live in California, so we can blame my fuel mixture problem on that! When I tour every year outside of CA, I have a new bike!And when I return home, I wonder why I still live here. It has gotten to the point where we should just call our gasoline "ethanol fortified with gas!" Bottom line is I must richen up the idle/slow circuit on my 1980 CX500 carbs. The carbs have been disassembled and cleaned several times. They are spotless. The main needles are shimmed up to richen the mid-upper range. The limiter caps on the idle mixture screws are bypassed, and turning the screws out until nearly falling out still gives me a very lean slow circuit. The air cutoff diaphragms are intact, with no holes. The intake manifolds have brand new O-rings. My 1984 Nighthawk's carbs have been cleaned a few times, but gradually started running so poorly on our gas that I went up two sizes on the slow speed jets. Just picked them up today. That got me thinking of doing that to my CX500, but the carb appears as if the slow speed jet is pressed into the carb, never to be removed. Is this correct? How else can I richen up the slow circuit if I cannot unscrew the slow jets? I have a pair of 1978 carbs (no accelerator pump) and I am so deperate I may try cleaning those up and trying them in hopes that the 1978 carbs might be jetted richer in the slow speed circuit. But I have no idea. The only other thought I have is if air could be leaking past the plastic bushings/washers on the throttle butterfly shaft. It is the only non-metal item which cannot be removed prior to carb cleaner dunking, and I always wondered how well they hold up to dunking in Berryman carb dip. Can air leak past the butterfly shaft if these are cracked out of sight? Any other suggestions on how to richen the slow speed circuit? Anybody with thoughts, I would appreciate also forwarding to my email, as I only have internet access once a week. Thanks.