Carburetor Settings for a Stihl Blower and Vacuum


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.

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 below!

Safe Basic Setting For Screws (H) & (L)

Easy2Start_actionshotCarefully screw the two adjusting Screws (H) & (L) down onto their seats (clockwise). Then:High speed adjusting screw (H): back off 1 complete turnLow speed adjusting screw (L): back off 1 complete turn

Basic Setting For Screw (LA)

Turn idle speed adjusting screw (LA) until the blower 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. Now 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. Now readjust screw (LA).

Stihl Blower Troubleshooting Guide

1. Compression Test – Can you lift the blower off the ground with the pull rope?2. Fuel Test- Remove air filter and cover and spray starter fluid in the carburetor and try to start. Use a 50:1 fuel mixture with premium fuel3. Spark Test – Remove spark plug clean with solvent & wire brush. Reconnect plug wire and let plug hang close to engine block (away from any gas) pull starter rope and look for spark, dim lighting makes it easier to see. If no spark replace plug and try again. Check off/on switch and wire coming from coil. If still no spark replace coil.4. The blower runs on starter fluid not on gas in tank. Check gas tank for old gas, empty old gas look for “syrup gunk” in the bottom of the tank, if present clean and rinse several times until clean (I use carburetor cleaner & gas and any brush that can reach in and not melt) Try to start with fresh gas mix. If it doesn’t start check and replace fuel line and pick-up. If it still doesn’t start remove carburetor and check manifold boot (tube between carburetor and engine) replace if needed and try to start. If it still doesn’t start remove carburetor, disassemble and clean carburetor, (clean outside of carburetor first) you may have to disassemble and soak in solvent over night try not to get solvent or carburetor cleaner on gaskets. Check gaskets, diaphragm gasket should be smooth and puffy not wrinkled or wilted if in doubt replace. Carburetor kits are around $8-$15 and include all gaskets, needle and spring. Reassemble (making sure all gaskets are positioned properly) and try to start if it still doesn’t start replace carburetor.Stihl Blowers & Vacuums Models on ebay; BG45 * BG55 * BG65 * BG85 * BR320 * BR340 * BR400 * BR420 * BR500 * BR550 * BR600 * SH55 * SH65 * SH85 * SR420

  • D. Clark

    I also want to thank the webmaster for this site. My Sithl blower doesn’t run at is maximum speed, cuts out sometime, and can be hard to start. I’m going to try the basics first like spark plug, air filter, but then this article will be great. Thank you

  • barringer

    My STIHL BR 340 blower will not start up, I tried starting fluid without luck.
    Its getting fire to the plug, the air filter is brand new, the fuel filter is new, the lines are new as well.
    I’ve been following oem starting steps: 3 pulls using choke (max) and it still will not start up.

    Ive never had a problem like this with these units, over the years ive probably owned 10-15 of the STIHL BR320 thru BR420C Magnums

  • Mr-dick

    I have a Stihl SH55 Blower and a FS38 Trimmer. They had difficulty running at top speed. On the advice of a dealer I removed the exhaust pipe ( a little short nipple with a screen on the inside) Holding the nipple in a vise or Vise grips using a propane torch heat up the nipple, it will burn off oil residue. Let it cool, reinsert the nipple, it runs like a charm.

  • B Pomering

    thanks a LOT !!! for that info , now mine runs like new again !!!

  • Lpardi70

    I have a br 320 stihl and it seems not to get a spark ….we take off the spark plug and its flooded it says here how to set the High and low speed air screw …Do I need a special tool to turn the screws please let me no ASAP thanks so much

  • Trudy16

    im try to find a daigram of a 420 stihl mistblower i cant get the carburetor off can ytou help me find a site

  • Michael

    Ive followed the directions for my still blower as it wont accelerate and sluggish when it tries. Ive checked the fuel and spark plug ….. any ideas?

  • Footer2000

    You most likely have a spark screen in the muffler with a threaded fitting. First check to be sure it is not plugged with carbon deposits. It is you will not accelerate effectively.

  • chris


  • chris

    should be after the air cleaner . thee screws on the base and then air cleaner comes off. unhook the throttle as well

  • Btschoppsr

    I replaced the primer bulb on my Stihl BG55 and now it won’t start. ??

  • ghost rider

    My br400 only generates a spark during the highest rpm point during a hard pull on the rope. Not before or after that point. My guess is the
    or magneto. Anyone have any ideas?

  • BottZ28

    If it is bogging down when you hit the throttle check the gas filter attached to the fuel line in the tank. It is tricky to get out.