But these all-position carbs are different than the ones on other equipment - does any of your other stuff get so rich it misfires (4-strokes) just by reducing the load a little bit? Reading plugs can be a useful long term check, but there's not really any practical way to run the saw without having it go through that so-rich-it-misfires zone, so your plug will have that on it too - it's cumulative based on all the conditions the plug was exposed to. Would you be able to tell that sometimes it's lean under those circumstances?
The all-position carburetor is the cause of many engine failures. Kind of like---it works in any position but not right in any. It is not a simple matter to get the carburetor calibrated right---you can't because of the design.
With two stroke motorcycle carburetors, IN GENERAL, the idle was controlled by air mixture screw in relation to an idle jet --idle to app. 1/4 throttle was controlled by the idle mixture in conjunction with the slide throttle cut-away, mid range was controlled by the needle jet in relation to the main jet. There was no High Speed adjustment. That had to be adjusted by position of needle in relation to main jet size. In all the transfer stages of this type carburetor, all systems overlapped.
I stated all this because the all-position carburetor doesn't work a fraction as good and it is so small with tiny fuel metering that the least bit of restriction can cause problems.
I think most people adjust their carburetors by "sound" and RPM while under no load conditions. I DON'T and I have never encountered an engine failure caused by a lean carburetor. I also differ from a lot of other people in that if I have a change in running condition, I clean the carburetor and return the adjustment screws exacthy as they were. Adjusting the carburetor only "maskes" the problem.
We just have to work with what we have untill a better carburetor is offered.
Sure--it's a lot of work to get it close to right but certinally less work then an engine failure!