Stihl chainsaws’ have three carburetor adjustment screws
(LA) Idle Speed screw - This controls the engine speed at idle. If set too low, the saw will die. If set too high the chain will run. This is dangerous.
(L) Low speed adjustment screw - This is the low speed jet. This is the adjustment that controls the air/fuel mixture at idle. Adjust this screw too rich and the chainsaw will blubber and die at idle speed. Adjust this screw too lean and the engine will starve. The saw will race or surge. An extremely lean adjustment will also cause the engine to die.
(H) High speed adjustment screw - This is the high speed jet. This is the adjustment that controls the air/fuel mixture at high RPMs. Adjust this screw too rich and the chainsaw will blubber, too lean and it will over rev
Safe Basic Settings
Screws (H) & (L) - Turn the adjustment Screws (H) & (L) down onto their seats (clockwise). Back them off 1 complete turn (counter-clockwise)
Screw (LA) - Turn (LA) Idle Speed screw until the chain stops. Then turn counter-clockwise one quarter of a turn.
Fine Tuning – Screw (L)
Erratic idling behavior; poor acceleration - Idle setting too lean; turn low speed adjusting screw (L) counterclockwise until engine runs and accelerates smoothly. Readjust screw (LA).
Exhaust smokes at idle speed -Idle speed setting too rich; turn low speed adjusting screw (L) clockwise until engine speed drops. Then turn screw back one quarter turn and check that engine still accelerates smoothly when you open the throttle. Readjust screw (LA).
Adjustment of the high speed adjusting screw(H)not only affects the power output but also the maximum off-load engine speed. If the setting is too lean (screw turned too far clockwise), the maximum permissible engine speed will be exceeded. This can cause engine damage, brought about by lack of lubrication and overheating in particular. Corrections to the setting of the high speed adjusting screw may be carried out only if an accurate tachometer is available to check the maximum engine speed of 13,000 rpm (with bar and correctly tensioned chain).
When the engine is tested at the factory the carburetor is set to obtain a slightly richer mixture to ensure that the cylinder bore and the bearings receive additional lubrication during the break-in period. This setting should be left as it is for the first three tank fillings. The high speed adjusting screw may then be turned no more than 1/4 turn clockwise (leaner mixture). Caution: The engine”s maximum permissible rpm must not be exceeded! Note that even slight alterations on the adjusting screws have a noticeable effect on the engine”s running behavior. Only carry out carburetor adjustments after cleaning the air filter and warming up the engine.
If you have no means of checking the maximum engine speed, do not set the high speed adjusting screw (H) any leaner by turning it (clockwise) beyond the basic setting Above!
This how-to works with a Husqvarna, husky, Jonsered, Poulan, McCulloch, Craftsman, Homelite, Echo chainsaws as well as a Stihl 009, 009L,011, 011T,012, 017, 018, 018C, 019, 019T, 020, 020AV, 020T, 021, 023, 024, 025, 026, 026 PRO, 028, 029, 034, 036, 036 PRO, 036 QS II, 039, 044, 046M, 066M, 088M, MS170, MS180C, MS191T, MS192T, MS200, MS200T, MS210, MS250, MS260, MS260 PRO, MS270, MS280, MS290, MS310, MS360, MS360 PRO, MS360 QS II, MS361, MS390, MS440, MS460, MS660, MS880, HT100, HT101, HT70, HT75 STIHL – Virtual factory visit