what exactly is saw doing when it 4 strokes

[tdi-rick]

Well i kinda do and dont understand. But i still believe a 2 stroke engine fires ever time its at TDC. Maybe thats where the ''4 stroking'' word come from. Sounds like its hittin ever other time. I know just enough to know i dont really know.

yep, but it's not a total misfire, ie. only firing every second TDC event.
I think it's firing, juts not burning properly and so you get the burble that you hear.

 

[komatsuvarna]

So what keeps a 2 stroke saw from running crazy rpms, like 22,000 rpm karts? I suppose if a saw had a unlimited coil and enough air and fuel flow it could run that many Rs. Providing the rest wouldnt fly apart. lol

 

[ShoerFast]

Fast air = low pressure, more effective fuel delivery.........

The 4-cycle/burble has more to do with the air : fuel mixture running out of oxygen at free-speed, as the pressure differential in the carburetor is higher at hi-speeds. (pig-rich, the saw can supply more fuel per air)

When a pig-rich saw hits wood, the engine slows and air :fuel ratio gets leaner as the lower air-flow has less effect on the carb-jetting/ air : fuel ratio.

The ragged sound is due to irregular scavenging from the incomplete O2 deprived combustion, and interrupted pressure wave as the flame goes out.

 

[bbdropshot]

Good info guys!!