There should be a high and low jets, which should be marked H and L screw them all the way in. don't tighten to tight it will mess up the end of jet. turn out 1 3/4 turns. Start saw and adjust from there.
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The fuel/air mixture in any gasoline-powered engine is regulated by the carburetor, and the carburetor in a Stihl chainsaw is factory-adjusted to provide the best performance.... You'll find three adjustment screws for the carburetor, usually located under the air filter cover.
Several reasons for that,
1. Air is getting into saw through leak in manifold
2. Carb idle/rev screw is set too high
3. Carb idle mixture screw is set too weak (uscrew it a tiny bit and check) See my other answer link below for advice on that:
4. Fuel filter in tank is partly blocked reducing fuel flow. They should be changed once a year on a domestic saw, more often on a professional saw.
5. The springs on the clutch are weak allowing it to engage at too low a speed.
Carburetor adjustment for efco 152 chainsaw
Hi, Rbmotorsport it should be noted that the "AIR FUEL" mixture screw adjustment "ONLY" manages your idle and has no effect on any other circuit also any intake leaks must be repaired before the A/F adjustment procedure can be performed otherwise you will never obtain a proper idle and you will waste a lot of time chasing the impossible. The A/F mixture screw's purpose is to fine tune the fuel charge entering the combustion chamber. The following applies to both 2 and 4 stroke engines:
1. The mixture screw may be sealed at the factory with a Welch Plug please review the following video for removal. https://www.youtube.com/watch?v=wAXcksgvDkM
2. The mixture screw manages a range of 3 complete 360-degree counterclockwise turns from the bottom/closed position.
3. The mixture screw should have a spring and o-ring for tension and sealing integrity.
4. Turn the mixture screw clockwise until it gently bottoms out, this makes the fuel charge very lean and the engine should not idle if it does then the pilot/idle jet is too big and needs to be replaced with the next size smaller.
5. Turn the mixture screw 1 and 1/2 turns counterclockwise to establish a baseline for starting the engine.
6. To fine-tune the idle circuit, adjust the mixture screw 1/4 turn in or out to achieve maximum idle RPM, wait 15 seconds between each adjustment for the idle to settle.
7. Never go past 3 full turns out this will make the fuel charge rich, foul plugs, and produce black smoke out of the exhaust, if the engine RPM keeps increasing past 3 turns the pilot/idle jet is too small and needs to be replaced with the next size larger.
7. After achieving maximum idle back out the mixture screw another 1/8 of a turn then adjust the throttle cable idle stop screw to 950-1050 RPM.
8. This procedure works great on 99% of all engines, for the 1% that demand a more robust throttle response on aftermarket monster fuel delivery systems additional tweaking outside the box may be necessary.
For more information about your issue and valuable "FREE" downloads that you will need please click on the blue links below. Good luck and have a wonderful day. Royal Star Airbox Modifications Setting carb fuel mixture screws Yamaha XVZ13TFL Service Manual OEM parts for Yamaha Yamaha Royal Star XVZ13CTV Owner Manual
Look for 3 adjustment screws on the carb. should be three total. 1 screw is for idle adjustment. the other 2 should be close to each other, one is low speed fuel/air mix and the other is high fuel/air mix. Adjust the low fuel/air mix screw until it will idle un-added with the throttle then adjust the idle on the throttle to get a good idle speed. Next adjust the High fuel/air mix until it gets the RPM's you want it to have. It should go from idle to high speed with out hesitation or cough. . Start with 1 1/2 turn out from all the way in. Be sure the filter is clean, You can use starting fluid or old school lighter fluid to aid starting if has been sitting for some time.
If you did nothing to the carburetor adjustments, are using a fresh (1.5 months or less) fuel mix with the same oil/fuel ratio, are operating at the same elevation, and the air filter is clean, there is a reason your saw is acting up.
The idle sdrew is usually separated fron the other 2 and probaly not fitted with an EPA limiter. HTH Lou