| | ok...update
As I noted in original post - My 1989 CR500 with a Keihin PJ carb would not idle. Worked great everywhere else - but no idle. I finally was able to work this out and get the bike to idle with the original carb. Took a lot of cussin' and about a case of beer, but success finally. Since the slide on the PJ - when the throttle is closed shuts off the throttle body completely, there is no way for air to flow into the carb except through the idle/choke circuit - of course the air screw too - so the problem had to be that the choke/idle plunger was not doing its job right by letting air flow though the passages on the side of the carb. Basically I think there were two issues, one .. the needle valve was binding and even though I was adjusting the choke knob to raise the needle to allow air flow - it was staying down shutting off the airflow. Also - before installing the plunger into the carb, it seems that the adjustment nut has to be midway in the threads. Right in the middle. I used a fine steel wool on the (for a better way to describe it) the brass plunger body and the needle on the valve to make sure it was clean and smooth. Look down in the carb body, and also make sure the hole where the brass body and needle go are smooth and clean also. I installed the standard jets in the carb.. I had a one step leaner main jet -which should not and would not make a bit of difference in the idle circuit, but just to be sure - and since I have had this bike for many years and it has lived in Texas (hot and dry and approx 800 feet above sea level) to NC - (wet and colder and 1200 to 2000 feet above sea level) and now in SC - (temps varies and at 360 feet above sea level) the carb had seen many jetting changes - so back to the OEM settings. Long story made short as possibly I can - over two days - many times starting this 500, and adjustments, I found that the air screw adjustment is pretty critical, as the motor would idle best...at 1 1/4 turns out (seems that the standard is 1 1/2 turns out) and with the plunger set into the carb with the nut set dead in the middle to start ---- key word - set in the middle.... I actually used a set of calipers to get the exact middle of the threads, used a light oil on the brass when installing the plunger, carefully snugged it down, just tight enough, and did not turn the choke knob at this time. Cranked the bike and then adjusted the air screw only a tiny 1/8 of a turn at a time. then make a small adjustment on the choke knob. Now this is when the motor is nice and hot - as in normal operating temps - and after approx 30 minutes I found the sweet spot. The motor would sit there and idle real nice -- no surges, no almost shutting off, it would just idle. Now granted I did not let it idle for longer than 5 minutes, but truthfully all I wanted was for it to idle for about 30 seconds - and it didn't need to idle that long as all I really need is a down to idle for a few seconds as in braking and entering a turn before turning the throttle back on. As most folks know .. unless your last name is Ward, Bailey, Johnson, Glover, Thorpe, Geboers, or Jobe, it is a rare 500 rider who holds a 500's throttle open all the time around a motocross track. Jeff Ward on his factory KX500 back in the late '80s - had his KX500 setup to not idle at all.... He used the throttle to steer the big KX around turns and he never shut off. It was his style. For me on the 89 CR500... as soon as I closed the throttle, the motor would shut off, and that was useless for me. Now... it works. On the downside, I still need to do a little tighter jetting, as before, this 89 500 would just jump up in revs as soon as the throttle was cracked open a hair, and rev out instantly, with the idle now working, and since this adjustment is affecting the pilot adjustments with different air flow, it is just not as sharp a response. Still good, but as I remember an article about jetting, there is a delicate balence in the transistion from off idle to the pilot when using the choke/idle knob as it also has an effect on the low end jetting. It is like changing the air screw mixture a bit. As a comparison, my 1994 CR500 is slow off the bottom compared to the 1989 CR500. Of course, that could be a number of things, the 94 is stone stock - cylinder, etc, and the 89 has a mild port job and polish. Coupled with that the 1985 CR500 was a brute and Honda (IMHO) really did not start to tame the CR500s until the 90s, the 89 model motor was still a helluva hitting motor. Both bikes - I have Pro Circuits pipes and silencers. Of course, truthfully, at 3rd gear, both bikes are making more HP than I can use, and it is a matter of hanging on for dear life at that point. I suppose that is why I short shift these bikes and avoid getting drilled into the ground. However, the nice thing about a CR500... you are only a blip of the throttle away from clearing any double at any speed. There is always instant HP on tap. So anyway - this how I managed to overcome the idle issue. I will be continuing to re-fine the jetting and if I run across any other issue/fixes I'll repost.