When I set these up after cleaning them for others, I set the individual adjuster screws as low as possible. This ensures the slides push hard to close all the way to the minimum. I 'bench sync' then by looking thru each one toward a bright light (bulb) and adjusting the screws of the 3 that are not closed to the most-closed one, until all are closed. They usually vary less than 1/2 turn of the screws across the whole set, and end up with just a couple or 3 threads of the adjusters above the nuts. Then I turn the idle setting screw inward to just barely open the set and ship them that way. No one that I know of has ever had the [carb-induced] high-idle problem from this setup.
The spark advance CAN (and on the 500/550 often DOES) cause a poor return-to-idle situation when the springs have softened to the point where they cannot pull the weights all the way in below 1200 RPM. The fix for this problem is to cut off at least 1/2 turn from each advancer spring and bend the last coil out 90 degrees to re-capture the weight. Often I have cut more than that.
So the slides should be essentially closed at idle? Not 4-5mm open?
I'm running my springs with 2 full coils cut off. Way too much for normal driving, feels sluggish until it advances and almost throws me off the back.
I took a look last night, realized my idle screw bracket was bent. I bent it straight and it still only has 1 or 2 turns of contact before it bottoms the spring out. Is that normal? That's with 4 threads showing on all of the adjusters - in other words I can bottom the idle screw out on the spring and the slides are only about 1-2mm open. Something seems wrong here.
You're right! There is something wrong there!
At idle, the slides are open about 0.4 to 0.6mm, just barely cracked open. The 750 is even less. The idle stop screw usually should be about 0.5 to 1.0 turns in from when it just touches the idle arm bracket, for about 1000 RPM idle. Many of the 550 arms seem to not allow for much more than that, just because of the geometry of the arm and the linkages, when they have worn out somewhat. This is because of all the little balls, sockets, springs, etc. that comprise the fancy setup. When they all wear a little bit, it adds up: the 500 version came with a washer under the spring on that screw, and after things wore in too far we just removed the washer to make up the needed stroke. So, it's not much distance.
I'd suggest setting up the slides first with the little adjuster screws set so that about 1-2 threads is poking out above the nut(s). Then see if this lets the slides close all the way (with the idle speed screw backed out). Then, bring in the idle speed screw so it just barely opens one of the slides (that might be the least-worn linkage) and then adjust the others to be open the same amount, using their little screw & nut adjusters. Then back off the idle speed screw to make sure they all will fully close together. Then, if the idle speed screw will not raise your idle high enough (it should reach up to 1500 RPM when screwed all the way in on a warm engine), either grind a little off the ends of the spring, or cut off one turn and install a flat washer under that end (to keep it from digging into stuff with the sharp end of the spring), and test it again.
This sounds tedious, but it's really not that bad once you figure out what you're chasing!
