Stihl Chainsaw Carburetor Tuning High and Low Screw

Fine Tuning Screw L Low Speed Fuel Adjustment Screw

The screw with the {L} marking is the Low Speed screw. Set the low speed fuel adjustment. Slowly turn in the screw until the engine surges or starves for fuel. Make a mental note of the position of the screwdriver slot. Now slowly turn the adjustment screw out and the engine should run better. Keep turning the screw until the engine starts to load up. Make a note of the position of the screwdriver slot and compare it to the position of the lean adjustment. Now slowly turn in the screw to a position where it idles the best. It should be about midway between the rich and lean settings. Slowly we lean the low speed adjuster by turning it in, till the idle climbs and it then starts to die. Then we go rich and hear the saw start to blubber and the RPM’s drop, almost to a point where it dies. The optimum setting is between these two extremes. If you think you’ve found just the right spot squeeze the throttle and the saw should rev up without any hesitation or stumbling.

Fine Tuning Screw H High Speed Fuel Adjustment Screw

Best method is to turn the {H} screw out 2 turns and fire up the engine. With the engine running full speed, adjust the {H} screw outwards until the engine exhaust burns slightly black and or blue smoke. Then turn the same screw inwards until the engine just starts to run too lean. This may be indicated by a drastically or slightly increased speed just before the engine appears to die slightly or totally. The center point between the 2 extremes is often times but not always, the best setting. On a 2 cycle engine. I adjust the high speed rich, causing it to slow down and bubble. Then we adjust it lean causing it to sound smoother and then it starts to starved Screw

  • Fdbgvdfsgvds

    very helpful!

  • Patrick

    I have a 270 stihl chainsaw,I start it, it runs, let it idle,it cuts off just like i turned it off,i have to pull it about 20 times to restart it ,;any ideas:?

  • Russell Locke

    My MS250 would probably start IF I could get the carb primed. It just loops the fuel back into the tank. I don’t see any lines off or any other obvious reasons. BTW, I always run the carb dry after using it and the saw has not been run for several months.

  • Stephen H

    Carb gumed up

  • elscorch

    my stihl 034 would do the same thing, start run and as soon as i let it idle it would die. Turns out it was flooding because the carb needed a rebuild. also the metering lever was adjusted wrong. it needs to be perfectly flush with the top of the metering depression(?). this solved my problem, now it runs and idles like a champ!

  • Joe

    The chain binds on my stihl ms250 whats wrong