Since it isn't a reed valve engine, any excessive blow-back through the carb on a running engine is usually due to wear on the piston skirt on the inlet side or stuck rings. With some engines, a bit of blow-back is normal under some operating conditions but has nothing to do with ignition timing.
Thanks for the info. As you say, these Kohler ignition systems are quite complex and appear to be either standard type coils with a separate module that triggers the coils or coils with the trigger module built in but I can't find any reference to how the timing of the trigger is achieved or if there is in fact a variable timing curve or just two fixed settings, one for idle and another for full throttle. Also, these ignitions are on a 12 volt battery based electrical system so it's possible it operates like a modern car engine where crankshaft position sensors give timing info to a master controller that determines when to produce the spark but that doesn't make sense as the coils are energized by flywheel magnets which means timing can only be varied by a few degrees and the spark can't occur before the magnets pass the coil legs. Sure would like to see design specs and complete ignition schematics.
As far as I know it varies with rpm. It's not an overly complicated system. Haven't ever seen any sort of timing maps though. No crank position sensors or anything like that. Really I think your thinking too simplistic. With not batteries we can run a spark system with computer controlled carb, with sensors. If we take the 500i for instance were doing a lot more. Possibly my expample of kohlers system was a bit over the top as battery power is readily available. But its not a stretch to have variable timing, or at least a variable curve.
I removed this reflector plate, but only partly, and now it seems she gets better.
You're right, there is no question about variable timing, pretty much all modern electronic coils have some form of it. The original discussion was about coils creating advance timing. In a simple chainsaw ignition where the coil is energized by a FW magnet sweeping past it, maximum advance is determined by the relationship of the coil legs, the magnets and TDC. The coil cannot produce a spark until the magnet has induced current in the coil so there can be no advance from this point. All the electronics in the coil can do is delay the point where an actual voltage spike occurs in the primary, there is no source of energy to produce a spark before the coil is energized by the magnets.
Interesting thing with this "reflector plate", are you attempting to stuff an exhaust pulse back into the cylinder like an expansion chamber does?
After a bit more research it seems most likely in older coils setting the max timing and retarding it is the way they did it. I did find some timing maps a guy posted. Interesting read.
I'll make video of my 361 with a timing light on it.
CDI
It's quite possible I'm just old and out of touch with latest technology. Can you show a circuit where the capacitor is discharged before a new cycle occurs and explain where it gets the timing info to fire? One of the systems with a separate timing coil? My discussion was limited to a 1 coil system. By the way, I was building CDI systems to replace points back when cars had distributors.
Thats kinda what I figured, I mean my kohler example is 30 odd years old by now.
It fired off a trigger. There's no reason to assume it's not integrated into the coil, or has to be separate. Firing the plug is independent of the magnets position. Really it just has to have a TDC reference as far as I know, but I admit my knowledge is pretty limited to the internal workings of the systems.
This plate has been welded on inside the muffler by Stihl factory, rough images are like these pic and a couple of drawings here. I said "reflector" for this, but original purpose seems to be a "defuser". I removed this "red-box-with-small-holes" partly.
If it gets a trigger from something integrated into the coil, it absolutely IS dependent on the position of the magnets. If it gets it's reference to TDC elsewhere as some do, its from a separate timing/pulser/trigger coil.
Looks like it's just a baffle that's meant to help attenuate the sound without adding too much restriction. A popular muffler mod is to enlarge all the holes to further reduce any restriction.
