Mostly because I'll get stalls on what seemed like a previously good tune, and at idle / low speed rather than WOT. This is leading me to believe that either the idle gap or LSN are set incorrectly. It runs fine in the higher throttle ranges, good performance and temps held between 200 and 250, so it feels like the HSN is set correctly.
At this point I think it's a mechanical fault somewhere that I'm trying to fix with tuning instead of troubleshooting.
I'm not really adjusting the idle gap every time so much as I am using it to trim-up the throttle during startup, and then I set it back to whatever it was before.
My Thunder Tiger Fish behaves the way you describe, in fact, they were so confident that you wouldn't need to adjust the needles that they used hexes instead of flat heads for the needles & idle screw, and even put in the manual that the carb should hold a tune once set, and so far it has.
The weather I run in varies from 60 deg F and 50% humidity to 90 F and 80% humidity, so I'm not surprised that I have to make some adjustments between outings.
I basically can't start my engines without preheating; I might be using that heat as a crutch instead of learning a more robust startup / tune.
If I do that and it idles too high, should I assume I have an air leak / cracked o-ring? That was kind of my experience. I was having trouble getting the idle down without outright stalling the engine. It'd run at a high idle, but perform inconsistently if I tried to lower the gap, although it was already quite "small"
Don't worry about the idle being too high, as long as the car is not rolling on its own, if it is, then just back it out a little. You want the idle to stay high so it does not die on you as you describe from being too rich.
Sometimes you may think it is, but there is still room to lean, as it could be your HSN affecting your LSN and idle by being too rich. Try leaning the HSN a bit more, or until you get lean bogs, this will not damage the engine, because you will richen it right back.
Once you are sure HSN is set, move onto LSN, richen it or leave as is, and see how the car behaves after sitting for about 5 seconds and you apply full sudden full throttle, if it hesitates and is sluggish with logs of smoke, start leaning the LSN until you get crisp and snappy take off after idling for 5 seconds. If you think the LSN is too lean after setting the HSN, then back it out and repeat the process.
I don't bother with fuel line pinching and then counting until it shuts off, for me this is amateur way of doing it and is never consistent.
When LSN is good, then as a last step, lower the idle until it purrs nicely....that's it.
When you take out the car out again, after you know you had a good tune, don't try and fiddle with LSN and idle, rather lean or richen the HSN, that will usually do the trick!
From experience, Kyosho engines really need a small idle gap, unlike HSP and HPI.
To check for air leaks I do a very simple test, before putting the carb into the engine, I attach a fuel intake tubing, close the air/fuel intake holes with my fingers and blow, you will hear air hissing if there was an air leak worthy of a concern.
I do repeat the same, once the carb is in the engine, blow and listen, and usually the front engine bearing will leak a bit of air, but this is normal, and should not be a concern, unless you have a puddle of fuel on your chassis after you are done running.
Make sure again, you plug all the obvious/normal air leak holes with you fingers.
Sometimes I can hear a hiss, but can't figure out where is coming from, I will submerge the whole engine into a bucket of water a and blow.
