How to Clean a 2 Cycle Engine Carburetor

by toolrepair

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Intro: How to Clean a 2 Cycle Engine Carburetor

Read this article for professional carburetor cleaning steps and advice. Learn why you may want to clean your tool's carburetor with or without a rebuild kit.

Cleaning a small engine carburetor usually gets done as part of a carburetor rebuild, but there are a number of reasons why cleaning a carburetor without rebuilding it is also a good idea for tool owners. 

Properly cleaning a 2-cycle engine carburetor means completely disassembling and reassembling the unit.

We explain the steps to disassemble and reassemble an example 2-cycle engine carburetor below, and we also explain the correct way to clean a carburetor while it's still disassembled.

Carburetor Disassembly Steps

This carburetor disassembly, cleaning, and rebuild demonstration is performed on a carburetor from a Ryobi 2-cycle grass trimmer. Steps for other carburetor cleanings will be similar to these.

Tip! Carburetors have many small parts. Keep carburetor parts organized in the order that they are removed (like in rows) to make reassembly fast and accurate.

STEP 1: Remove the Bottom Plate


On The Bottom Side of the Carburetor,

Unscrew the two screws that affix the lower cover plate to the carburetor body.The bottom plate is held on by four screws for some carburetor models.

STEP 2: Remove the Diaphragm and Diaphragm Gasket--Separate Them If Needed.

The carburetor diaphragm will come off easily after the bottom plate is removed.

The diaphragm gasket will often stick to the diaphragm when removing it from the carburetor body. If the diaphragm and diaphragm gasket are stuck together, they must be carefully separated from one another to be cleaned later.

STEP 3: Remove the Needle Valve Mechanism

The needle valve mechanism consists of three parts: a needle, a lever, and a spring.

It will be visible in the body of the carburetor after the diaphragm is removed.

The needle valve mechanism is held into place by a retaining screw.

Unscrew the needle valve retaining screw to release the mechanism from the body of the carburetor.

Make sure to hold the spring-loaded mechanism in place as you remove the screw. This will stop the valve parts from flying across the workbench.

STEP 4: Remove the Primer Bulb and Its Retaining Plate

The Primer Bulb Side of the Carburetor

Remember to keep the carburetor parts organized as you go. This is a good place in the disassembly to start a new row of parts.

The primer bulb is held onto the primer base with the help of a retaining plate. Two screws affix the primer bulb retaining plate to the primer base.

Remove the two screws that hold the primer bulb retaining plate to the primer base.

STEP 5: Push the Primer Bulb From Its Retaining Plate


STEP 6: Remove the Primer Base and Carburetor Reed Valve

Removing the primer base retaining screws frees up the primer base from the carburetor body.

Set the primer base aside for cleaning. Look for a thin reed valve piece between the primer base and the carburetor body.

Handle the reed valve piece with care. It is important to the operation of the carburetor and very delicate.

If a fragile piece like this one is damaged on a carburetor that lacks a rebuild kit, the entire carburetor will most likely have to be replaced.

After following these steps, all the small pieces of the carburetor are now removed from the carburetor body and are ready for cleaning.

STEP 7: Cleaning the Carburetor

For this part, you'll need:
  • a pan
  • a can of carburetor cleaner
  • a towel, and
  • compressed air (if available)

The procedure for cleaning each part of the carb is the same:

1. Clean the outside of the part. 

2. Clean the inside of the part.

3. Dry the part.

4. Be very careful with sensitive parts. 

Start with the body of the carburetor and don't be afraid to use a lot of cleaner on it.

Take advantage of the openings in the carburetor body to clean its fuel pathways.

Make sure to point orifice outlets away from you when you do this!

Thoroughly air dry the carb body with compressed air (f compressed air is available) and set in on a towel to continue drying.

Move on to the other durable pieces of the carburetor.

The internal orifices of the primer bulb base require cleaning just like those of the carburetor body.

Cleaning Delicate Carburetor Components

There are a few pieces of the carburetor that need extra consideration when cleaning them, including the reed valve piece, the screen filter on the carburetor body (see below), and the carburetor diaphragm.

  • That thin reed valve piece that goes between the carb body and the primer base must be cleaned and handled carefully.

Use as little carburetor fluid as possible and spray it at low pressure to avoid damaging the piece.

Quickly dry the reed valve on a clean towel after gently spraying it with cleaner.

  • Many carburetor designs include a small screen filter on the carburetor body.

This filter is easily damaged when removed. Leaving it in place is usually the best choice when replacement filters are not available.

  • The carburetor diaphragm is another piece that is often too delicate for rigorous cleaning.

The diaphragm is made of thin rubber in the case of our Ryobi demonstration carburetor. Because rebuild kits aren't available to replace it if it were damaged during cleaning, it should only be cleaned when absolutely necessary.

STEP 8: Steps to Reassemble the Carburetor

Most of steps to reassemble a carburetor are self-explanatory in that you simply replace components in the reverse order that you removed them.

Replacing the needle valve mechanism is the trickiest step when reassembling the Ryobi 2-stroke engine carburetor that we use for demonstration in this article. 

Here are the steps for replacing the needle valve mechanism:

1. Place the needle on the lever.

This carburetor's needle valve lever has a forked portion on it. The top of the needle fits into the forked portion of the lever as pictured below.

2. Replace the needle valve spring.

Just place the spring back into it's slot in the carburetor body.

3. Drop the needle into the valve jet.

The needle valve lever will rest on top of the spring when the needled is dropped into position.

4. Reinstall the needle valve retaining screw.

Hold the needle valve mechanism in place with your finger once it is aligned into position.

Return the valve retaining screw while holding the mechanism down.

The rest of the carburetor reassembly should be pretty straight forward if care was taken to keep parts organized while it was dismantled. 

Watch this article's video demonstration of this procedure for detailed reassembly steps!

Ryobi Carburetors and Cleaning Maintenance

Owning a Ryobi gas-powered tool is usually a good reason to perform a carburetor cleaning without the help of a rebuild kit. This is because carburetor rebuild kits are not available for most Ryobi 2-cycle tools.

Carburetor rebuild kits include replacement parts for many of a carburetor's small, inexpensive, easily-worn parts. When used in a traditional cleaning and carb rebuild, these kits get an old carburetor running like new with little effort on the part of the tool owner.

Additionally, the availability of replacement carburetor parts takes some pressure off of the person performing the rebuild, because delicate parts that may be accidentally damaged during the rebuild can easily be found and reinstalled.

Maintaining the life of a carburetor takes extra care when carburetor rebuild kits are not available, like in the case of Ryobi tools.

When the small parts of the carb can't be replaced inexpensively, the best way to maintain the performance of the carburetor is to dismantle and carefully clean each part.

Carburetor rebuild kits can occasionally become unavailable for tools of every make, but we chose to perform this article and video's demonstrations on a Ryobi carburetor because of how commonly rebuild kits are not available for them. 

Conclusion

If you're looking to check the availability of carburetor rebuild kits for your gas-powered tool, type your tool's model number in the search field at the top of this page.

Your tool's parts page will have available rebuild kits listed on its parts page just below its breakdown diagram!

You can also search for carburetor rebuild kits by visiting our Small Engine Parts page here at eReplacementParts.com

16 Comments

rgrieve44 6 years ago

Lost screen..

I have a Ryobi trimmer that won't start. As part of the diagnosis, I cleaned the carb. In doing so, I did find some gunk - unfortunately it still won't start, so diagnosis is still ongoing. In any case, while cleaning the carb, I used compressed air, and blew out the screen. At the time I thought I saw something fly out, but I didn't clue into the fact that it was the screen. Now I can't find it. What are the consequences of running without the screen? I will try to see if I can get a replacement screen at the local shop, but I suspect I'll need a whole new carb.

GeorgeF65 7 years ago

Nothing more frusturating for the average individual than a 2 cycle engine that will note start or run well.. If you have compression and Spark those two cycles run very well with a bit of Carb work that anyone can do.

99% of Carb problems in our Diagnostics Lab 5 years years ago were traced to bad machining of the flapper valve Aluminum surface. That surface so important to proper flapper valve seating is a rough sanded factory surface comparable to a 180 grit sand job . Just look at those machining marks in there.

Take apart only that flapper valve side of the Carp. Then take and polish that entire Aluminum surface with a 1500 grit Auto polishing paper glued to a flat board .

The flapper valves will it seat properly and 2 cycle engines become easy starters . Many of our test engines starting with one or two pulls 5 years later. Don't be fooled by Carb replacement garble Resurface that Aluminum surface as above and your starting problems will be gone.

RandyW67 7 years ago

I heard that carb cleaner will ruin the plastic and rubber gaskets and O-rings in a carburetor. Is that true? If so, please update the instructions with that warning. Thanks!

PeterM30 8 years ago

I have a Blue Max Chainsaw and it was running pretty well until yesterday, I think I mixed too-rich fuel mixture. It was almost stalling when I gave it gas, then eventually it gave up the ghost. I have replaced the spark plug, fuel filter, checked the muffler and spark arrestor and cleaned everything up fairly well, but it will not start, period. I even used ether starting spray, which usually starts anything, but nada. My carburetor does not look anything like the one in the instructions. It's smaller, and it look pretty clean. Should I take it out and clean?? I do get a spark across the plug, btw.

Any help would be appreciated, thanks!

-Peter

kmahony2 8 years ago

you might be after clogging the exhaust if you were using this oil rich mixture for a while. I'd say remove the exhaust and apply heat using a torch first before dissembling the carb. there will be alot of fumes so obviously do this outdoors.

Gkempf 10 years ago

I have a craftsmano weed eater with out a primer bulb,carburetor been off the the unite for a while,I've replaced the carb,but now I don't remminber how the fuel li

oakback 13 years ago

I recently did this for a Stihl trimmer, which has a Walbro carb (though it looks just like the one in this instructable). I bought a parts kit from a location dealership and did pretty much everything explained here, except replaced old parts with new.

For me, the hard part is tuning the thing afterward. I still haven't been able to get it to run right and idle right (I can get it to do one or the other), even after finding the factory tuning specs online and following that.

H454 12 years ago

There Is one screw for idle(I) and one for everything from idle and hirer(H). Set the idle first than the high, after its warmed up. If you Messed up it totally, turn all in (to the right) than back about 1 - 1.5 turns. Then go from there (plus) or (-).  Somtimes there is three screws - Idle(I), LOW (L)-first half of RPM range, and High (H)-upper half RPM range. Tune in order of lowest RPM to Highest.

Also check your air filter, gas line, and important and often missed - the fuel tank breather tube (I have a Stihl chain saw that always has problems with breather tube).A bad breather tube creates a vacuum lock, their by stopping fuel flow.

Check the spark for a bright blue consistent spark.

Also Try fine tuning oil/gas ratios -That can have have a Very noticeable effect on tuning and performance( especially in smaller engines)- more oil tends to run a little richer.

RCline 13 years ago

It's not a good idea to soak down rubber gaskets/diaphragms with carb cleaner. It will weaken them and sometimes destroy them. Carb cleaner is nasty stuff. I had to learn the hard way.

toolrepair 13 years ago

The intended purpose of the article is to demonstrate how to clean a carburetor when a rebuild kit is unavailable. In this situation the risk of any damage while cleaning the carburetor is greatly outweighed by the high cost of a replacement carburetor. As far as carburetor cleaner potentially causing damage to the rubber components in the carburetor, that is true and a real risk. In my experience I have found some carb cleaners to be much more prone to causing this damage than others. It seems that the higher quality carb cleaners greatly reduce the risk of this type of damage.

Tool Repair Guru
eReplacementParts.com

invisiblelight386 13 years ago

I Work at a small engine repair shop and we work with Ryobi equipment fairly often and we are able to get rebuild kits for the carburetors. Most small engines use ether Walbro or Zama carburetors. From my experience the most common reason for a dysfunctional carburetor is the filter screen in the carb body getting clogged or the lever that opens the needle is bent too much in the wrong direction letting too much or not enough fuel in to the carb. I might have missed it but I did not see anything on resetting the hight of this lever. Depending on the type of carburetor this hight can very but in most Zama carbs the lever is flush with the top of the carb body. On a Walbro it is recessed a little bit below the top. Each company has its own metering gage for its carburetors.     

toolrepair 13 years ago

We also made an instructable of Mark with eReplacementParts.com showing you how to properly do this in a video! Hope it helps, I know some of us don't like to read as much as watch :)

Click Here for the Video

jptrsn 13 years ago

Really good: clear instructions, and good photos. I'll likely give this a try on my trimmer once the grass stops growing!

I second the vote for a 4-cycle tutorial for the mower that goes with the trimmer!

biker_trash_1340 13 years ago

Great Job. A lot of people are afraid to tear into a carb. This enplanes it very well.... 4 cycle next?

toolrepair 13 years ago

Thanks for the support @biker_trash_1340 -> Hopefully we can find the time to get a 4 cycle guide up here :)

Tool Guru
eReplacementParts.com