How to clean and adjust Two Cycle Carburetors


Reader Kenneth B. writes…

“An article on carbs would be helpful. How to adjust them and clean them…”

Thanks, Ken.


Ya know, it’s funny.

It seems like at least once a week, we get a guy in here who is experienced in multiple facets of auto mechanics. This is a guy who can strip down and replace the posi-trac rear-end on a Plymouth in record time! With their eyes closed! With a full bladder! I know this because they always make a point of telling me so.

But then they drop a chainsaw on my counter. Then they stand there shamefaced and chagrined.

“I think it might be the carb. I don’t know nothing bout these things.”

Double negatives. You gotta love them.

Now, I’m saying this, not based on personal experience but out of sheer ignorance of automotive mechanics. But, how can a man who knows how to rebuild an automobile engine with a pair of pliers and a stick of gum be completely lost on a two cycle carb?

I mean, car stuff is so much bigger and more complicated with more stuff and moving thingy’s and…..well… stuff.

Clearly I know enough to know I don’t know enough. There’s clearly a difference, and I can accept that. But, when it comes to cleaning and re-building their little cousins…even I can figure that out.

I think…

To give your two cycle carburetor the once over, knowing what goes where is the name of the game.


Disclaimer: The information provided below is not presented as the one and only, end all-be all, works the same every single time (so its our fault if it doesn’t work) instruction manual on how to repair every two cycle carburetor ever made. This is a generalized tutorial, which will (hopefully) provide a familiarization with the components of the basic, two cycle carburetor.


I feel compelled to say that because from time to time we run into folks that seem to believe that because its on a web site, it somehow re-writes reality. The truth is, you have your carburetor in hand. I can’t see it, so go with what you know. When in doubt, give us a shout.

So, here we go…

You’re going to need

Carburetor Cleaner- A good, aerosol cleaner will work.

A Phillips head screwdriver

 A clean, well lit place to work

A spill container that will minimize the splash from the carburetor cleaner

   A clean rag

Safety glasses or goggles. Latex gloves aren’t a bad idea either.

Compressed air to dry the carb, or a clean place to allow it to air dry

The correct rebuild or gasket / diaphragm kit for your carburetor- 9 out of 10 times, your carburetor will be manufactured by one of two companies: Zama or Walbro. Lawnmowerpros.com can help you determine which carburetor repair kit is right for your carburetor.

There are probably lots of other tools designed to complete this task. I don’t know that they are truly necessary…maybe they are. But so far, I’ve managed to muddle through without most of them.


REMOVING THE CARBURETOR

Lets start by removing the carb from the equipment.

This will most likely involve removing the air filter and air filter base and disconnecting the fuel lines and possibly a cable.

Often, we’re looking at a couple of bolts holding the thing onto the engine. Just be careful, don’t strip the bolts. When in doubt, give us a shout.

Be mindful of any cables or fuel lines that may be attached to the carb. You’re going to have to reconnect those, so it might not hurt to mark them before removing them.

The outside of your carburetor is probably a little dirty. So, let’s take her over to your cleaning area and spray the mess off of it. Liberal use is recommended.

Remember, any debris left on the outside of the carb can get inside of the carb, so be thorough.


DISASSEMBLING THE CARBURETOR

There are varying assemblies for these carburetors. The important thing to remember is to lay the parts out in order as you remove them. They’re tiny, they disappear easily  and its way too easy to get confused. Oh, and finding assembly diagrams may be helpful before you begin.

Check out the following:     Walbro        Zama


Two-Cycle-Carb-Breakdown


Let’s start with the metering diaphragm cover, which is at the side opposite of the primer bulb.

  • Remove the two / four retaining screws and the cover itself. It may be stuck on there a bit, but a light tap on the side or prying it from the carb may be in order.
  • Remove the diaphragm. That’s the weird looking little film like part. Probably black, might have a little metal disc in the center of it (See Image).
  • If you’re installing a new one, go ahead and discard the old one now. If not, set it in order with the other parts; we’ll get to that later.

Next is the diaphragm and gasket.

Removing the gasket may damage it, so before you remove it, you need to decide if you’re going to reuse it or replace it.

  • Take a good look at it. If you intend to reuse it, you may want to just keep it where it is. If it’s in good shape, leave it be.
  • However, if its in bad shape, or if you intend to install a new one, just go ahead; remove it and discard it now.

You’ll be looking at the needle and spring now. Here’s where the screw driver comes in.

  • Place a finger over the needle and needle arm. We don’t need that thing shooting across the shop when you remove the retaining screw.
  • Remove the retaining screw and set it in order.
  • The needle, arm and spring will remove easily now. Set them in their respective places.

ZAMA 0057030 PRIMER BULB

Now, let’s flip it over and remove the primer bulb.

 

  • The primer bulb will be held in with a metal plate and two / four small retaining screws.
  • Remove the screws and set them aside.
  • Remove the retaining plate. The primer bulb will come with it.
  • Inspect your primer bulb. If it’s in good shape, you may want to keep it. If not, pop the old one out of the hole in the retaining plate and push a new one in.

My advice is, if its more than a year old just replace it. I mean, you have the thing taken apart and you’re going to have to replace it some time so why not knock it out now?                  Just one guy talkin.


The next part should be the primer base. Old gas gets sticky, so you may have to gently pry it off.

  • Remove the primer base.
  • Once again, we may have one or more thin, mylar diaphragms or reed valves. Carefully peel them off. if they come apart, time to get out the old rebuild kit.
  • Beneath the reed valve is another gasket. Refer to the gasket above.
  • Inspect them for damage. Discoloration, tearing, cracks, shmutz, any of those things and it’s time to replace them.

CLEANING THE CARBURETOR BODY

So, we’ve effectively stripped the carburetor down to its base components. Well done! Now, let’s move the carburetor body back to our cleaning area and work that thing over.

Time to put on your eye wear.

  • Place the carburetor inside of your spray container.
  • Using the carburetor cleaner liberally, remove any dust or debris. Make sure that you get all the nooks and cranny’s cuz “dirts causes troubles”!

Warning: There are tiny little holes all over your carburetor that you’re going to want to clean out. Just be aware that what goes into one hole is going to come spraying out another hole, and not necessarily in the direction you might think. Those things are like a tiny, little water slides inside there!

WALBRO 140-70-8 FUEL INLET SCREENYou may discover a small filter screen recessed into the carburetor body. It could become damage during removal, so if you intend to take it out, make sure your rebuild kit comes with a new one. Otherwise, if it ain’t broke – don’t fix it.

Compressed air is a great way to speed up the drying process. If you don’t have compressed air, best to just let it air dry in a well ventilated area.

Carburetor cleaner is flammable! Do not dry with a hair dryer or open source of flame!

 


CLEANING THE PRIMER BASE

  • Once again, let’s head over to the cleaning area.
  • Use the carb cleaner to clean the primer base, once again paying attention to all of the little openings.
  • Wash, dry, all that jazz. Now set it in its spot.

CLEANING THE DIAPHRAGM AND GASKET

These are tiny little paper and mylar pieces so we want to be extra careful.

Visually inspect the diaphragm(s) and gasket. If they look ok (intact, re-usable), and you’re not replacing them, then set them aside to re-install later.

They’re pretty delicate, so I don’t recommend trying to clean them unless they’re visually corroded or gummed up. If you’re going to clean them, remember: they’re tiny and plastic so be careful. A little carb cleaner, a gentle wipe with your clean cloth and you should be good.


PUTTING IT ALL BACK TOGETHER
If you’ve taken my advice then all of your parts are laid out in the order in which they were removed. Now, all you have to do is go back down the line and put it all back together in the order it was laid out.

If not, here’s a guide:

Reinstall needle spring
Reinstall needle, lever and retaining screw
Reinstall diaphragm
Reinstall diaphragm gasket
Reinstall base plate
Reinstall base plate screws
Reinstall mylar reed valve
Reinstall primer base
Reinstall primer bulb
Reinstall retaining plate
Reinstall retaining plate screws


So there you go. You have a nice, clean, sparkling two cycle carburetor.

Put her back on the machine and lets see if that took care of it. If she’s purring like a kitten, then your carb could be salvaged with a good cleaning. Well done! If not, it may be time to get a new carburetor or have a technician look at it.

We hope this was informative and helpful. If anyone out there has an great tips on how to make this even easier, send them in. We’re a small army of small engine experts! Let’s share the info!

This carb…is…clear! Poltergeist! Ha!

-Bill


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Bill Brown

Bill Brown

Bill is the head of content creation for the LawnMowerPros Blog and DIY section. He’s been in the Outdoor Power Equipment Industry for years and he’s still learning new things everyday. You can often find him creating featured articles, DIY guides, videos, graphics and much more.