How to Start a Stubborn Weed Trimmer With a Thimble and Some Gas

Reviewed by Ben Barkan

Last Updated: April 29, 2024

Weed trimmers can be a pain to start at times, and when they start to get old, sometimes they need a little help to get some gas into the cylinder head. Some use starting fluid for this, but a small amount of gas can work as well, as explained in this article.

Steps

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Do a quick check to satisfy yourself.^{[1]
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Take off the spark plug with a spark plug wrench.

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The rim should be silver and not black, and the point should not have build-up on it either. If the rim needs to be cleaned, scrape off the deposits with steel wool or a use small flat head screwdriver. Be careful not to break the white ceramic insulator.^{[2]
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It should rev up a little then stop because choke is still on.
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Pull the rope again with choke off a few times and the engine should start.
- If the engine does not start, replace the spark plug with a new one, as this could be the problem. (The old spark plug has a number on it, so write it down before going to the store).
If it still does not start, it could be the carb is gunked with deposits, in which you will need at this point, some carb cleaner.^{[3]
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Clean the carb. To clean the carb, remove the carb cover and spray off the jets, making sure that they are clean and unobstructed.^{[4]
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- Then take off the primer cap from the line and spray carb cleaner down the tube where the cap was attached and replace the primer.
- Press a few times, forcing the carb cleaner in the line into the carb.
- Repeat this process a few times.
This is a screen that prevents hot particles from escaping the muffler, which can cause a fire. If it is blocked, remove it and scrape with a wire brush or a piece of wood, then replace it.^{[5]
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Also note whether after you have put a few drops of gas in the cylinder, and replaced the spark plug, it fires up for a little but does not run. If so, this could mean the carb is blocked, because gas is not getting from the carb to the cylinder, and the only thing that's making it run for a bit, is the little gas you put in the cylinder. If it does not run at all, it is usually because the spark plug is either spent or dirty.
Press primer bulb a few times forcing excess gas in line to run into carb, and then pull starter rope a few times forcing all the gas out. Excess gas sitting in the line and in carb over the winter causes blockage, so always empty and clean when not in use for extended periods.

Community Q&A

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Question

What can cause the trimmer to stall after pulling the trigger?

Community Answer

Bad air/fuel mixture. Dirty gas, often water in carb. Clogged muffler screen. Clogged air filter. Spool head could be binding from long weeds wrapped around.

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Today's ethanol gasoline is a big problem for small engines, two-stroke and four-stroke, especially engines that are not used every day or two. Ethanol will separate and go to the bottom of the tank. It will also leave a gummy residue or "varnish" on carburetor parts and ports. Some say this is the cause of most small engine problems today. These small carburetors have small ports, needle jets, screen filters, and holes that can be blocked or partially blocked by the smallest impurities.

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Replace the weighted filter in the gas tank on weed trimmers. These filters are easy to remove with a small hook on the end of a "coat hanger" wire. The weighted filter is on a length of tubing in the gas tank and allowed to reach the bottom of the tank no matter how you hold the trimmer. The filter can easily become clogged with all kinds of debris.

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To prevent this problem in your engines, use a gasoline additive in every gas can before you fill any small engine gas tanks. Some additives will prevent the problems; some will help remove the varnish and gum. These additives are inexpensive and cheap insurance.

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Warnings

Don't try this if the engine has been running and hot. If you spill gas, it could ignite if it contacts the hot engine.

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