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How To Adjust The High & Low Speed Screw On String Trimmers Carburetor

by JEREMY HIPA 08 Jul 2022 0 Comments

All small engine equipment will become worn and dull over time. Take the weed eater as an example: you will need to adjust the carburetor speed to get a good trigger response and cutting performance after a session. Here is a simple fine-tune instruction on how to correctly adjust your carburetor on the weed eater.

This method is typically for string trimmers but may not be suitable for chainsaws and other small engine equipment.

Step 1 Preparation

Safety First

Ensure you are in a well-ventilated area, outside or inside, with all doors and windows opened. Never do this in an enclosed area.


  1. A big flat screwdriver
  2. A little screwdriver

Step 2 Reset the Screws

First of all, you are supposed to take off the air filter and put those nuts back on to hold the carburetor on, because the air filter may influence your judgement of the engine reaction when you are tuning.

Use the little screwdriver to slightly the high-speed screw and the low-speed screw in until they are lightly seated, and turn both of the screws back out 1/4 turn. (Small tips: do not screw them in so tight that it may damage the carburetor. )

Step 3 Adjustment

Initially, you are supposed to get the limiter caps off by using the flat screwdriver to respectively stick into the crack between the carburetor and the limiter cap. Then twist the screwdriver, and the limiter cap will pop off.

Before turning, it is also necessary to turn on your string trimmer and warm it up for a minute.

The High-Speed Screw

We will start with the high-speed screw rather than the low-speed screw on a string trimmer. However, low-speed adjustment is the top priority on chainsaws.

  1. Press and hold the trigger down to run as fast as it can.
  2. Use the little screwdriver to turn the high-speed in and out until you find the spot where the string trimmer running the fastest.
  3. Unscrewthe high-speed screw slowly until you hear the RPM (revolution per minute) start to drop, then turn the screw back in again until you hear the RPM just come up to a position where it is making the humming sound.

That is the ideal position of the high-speed screw.

The Low-Speed Screw

Here, you do not need to hold on tothe trigger, you just need to leave it at If the string trimmer does not idle, you just need to turn the low-speed screw in until it idles.

  1. Similar to the high-speed screw, turn the low-speed screw in and out until you find the sweet spot where the string trimmer idling the fastest.
  2. Turn the low-speed screw out very slowly until you hear the RPM just start to drop.
  3. Leaveit there, do not turn it back in.

Finally, you will receive an excellent trigger reaction when you punch the trigger again.

Product Recommendation

1. HIPA 2-Stroke Carburetor Adjustment Kit

HIPA Carburetor adjustment tool set with cleaning kit for string trimmer

HIPA Carburetor adjustment tool set with spark plug for string trimmer

Hipa's parts kits make it quick and easy to maintain or restore your lawn and garden equipment. Whether you need replacement parts, tools, or help, has the small machine solution for you.

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