How-To Special: Rebuild a Small Outboard Carburetor

If something’s gumming up the works in your small outboard’s carburetor—literally—it’s probably time for a rebuild.

5th December 2013.
By Lenny Rudow

An aching back, sore shoulders, blisters between your fingers, and a frustration-induced headache are all signs of a small outboard carburetor gone bad. Yes, you’ve been tugging and tugging and tugging on that starter cord to no avail. You’re stuck at the dock, dead in the water, and done boating for the day. You’ve checked the fuel supply, cleaned the air filter, made sure the plugs are firing, and kicked the lower unit once or twice for good measure. It’s time for a carburetor rebuild.

(Got a different outboard issue? Read 5 Outboard Engine Quick Fix Tips)

small outboard engine running

Don’t let a crappy carburetor ruin your fun – keep that small outboard humming, with a carb rebuild.

Thanks to the advent of ethanol, the need to rebuild carburetors has become even more common than in past years. When that quick-deteriorating fuel sits for too long—which is usually a matter of weeks, not months—it’ll leave way too much gunk in the carb for one of those spray cleaners to get the job done.

Wait a sec—is this really a task you can tackle on your own? Don’t worry. All you need to rebuild that carburetor is a stock of 5052 H-36 milled aluminum, an acetylene welding torch, $5,000 in parts, and a machine shop. Nah, just kidding. Truth be told, “re-building” the carb on a small outboard is actually just cleaning it thoroughly, and installing a few new gaskets and parts. In fact, any moderately-competent do-it-yourselfer can handle this job. Ready to get started?

Let’s Play Operation

First, you’ll need to remove the carburetor from the engine. Identifying it is simple: just follow the throttle cable, and look for the section of the engine it’s attached to. You’ve found your carb. But before you can take it off, you’ll need to remove the throttle cable, fuel line, and any other wires or air filters that may be attached to it (this will vary, depending on the size and complexity of the engine). This is sort of like playing the game Operation, because you’ll need to be careful not to drop any of the pins, screws, and clamps that may be holding those items in place. If you do, there’s a good chance they’ll disappear into the black hole of outboard engine nooks and crannies.

remove carburetor from an outboard

Pulling the carburetor is as simple as removing a few cables and a hose or two, then spinning out a couple of bolts.

TIP: Before you remove anything, grab your cell phone and snap off a close-up picture of the carburetor and all of its attachments. If you have any confusion when re-assembling things later, that picture can be a life-saver.

With all that gadgetry out of the way, you should now be able to identify and remove the bolts that are holding the carburetor in place. You’ve got it free? Good job. Now take it into a controlled work-space, like your basement or garage. Then, disassemble the main parts of the carburetor; on a small, simple outboard, you’ll have just two or three pieces. Once they’re separated the bowl will be exposed and you can remove the carburetor’s non-metallic parts, like the float and gaskets. Again, take a picture or two with your cell phone to make yourself a map of where the pieces go as you take them apart.

rebuild carburetor

Broken down into two main parts, the carburetor bowl and float are exposed.

Bath Time

Most of those non-metallic parts will be replaced with the items in your carburetor rebuild kit (which you can get either from the engine manufacturer or Sierra Marine), but you want to make absolutely sure everything plastic is removed before you take the next step: submerging the carburetor in a solvent bath. Otherwise, those parts can literally melt in the bath and contaminate the solvent.

This part of the  job is easiest if you get a large can of GUNK Carburetor Dip or a similar solvent/cleaner, which comes with a metal strainer basket inside the can—you don’t want to have to reach around and fish out carb parts, or your hand will end up minus a layer or two of skin.

TIP: This stuff isn’t just harmful if it gets on your skin, it also creates some atrocious fumes. Once the parts are in the can, re-seal it to keep those vicious vapors from filling up your workspace.

While your carburetor pieces-parts are percolating in that brew, go watch some football or sit down to a movie, and give the cleaner a few hours to do its thing. During half-time, pull out the strainer and allow the parts to drain. This will help rinse away some of the crud. Then, drop them back into the solvent bath for another hour or two.

After the carburetor has had plenty of soak-time, remove the strainer, set the parts out on a towel, and let them drain thoroughly. Then give them a close visual inspection for gum or crud, to make sure the bath has eaten it all away. If you spot any remaining gunk, scrub it off with an old toothbrush and give that part another dunk or two in the cleaner.

For the final stage of cleaning, you’ll need an aerosol can of regular carb cleaner with one of those little red nozzle tubes on the end. Use it to blast out every little hole, passage, and corner you can find. Then use a can of compressed air, to blow out any remaining carb cleaner. Once the metal parts are gleaming and 100-percent contamination-free, you’re ready to set them back on the towel until they’ve dried off again.

Jigsaw Puzzle

It’s time to put all of those carburetor parts back together, into one functioning unit. Luckily this is a lot easier than it sounds, because all of the parts in your rebuild kit will fit into one place and one place only. Replace the float and needle first, since these need to be secure before you can replace the gaskets and O-rings. Is it getting a bit confusing? No worries—as you put those puzzle parts back together use the pictures you took earlier as a reference, if need be.

rebuild a carburetor

When you rebuild a carburetor the difference between old and new parts can be amazing – the gasket you see to the right was just two years old, but had clearly deteriorated quite a bit.

With the reconstituted carburetor in-hand, you’re ready to mount the unit back onto your outboard. Replace the main bolts first, then re-attach the accessory units you removed. This is a good time to clean out any of the engine’s internal fuel and air filters, too, so all your hard work doesn’t get un-done in short order.

rebuilt carburetor

After you replace the rebuilt carburetor and re-attach all the lines and cables, don’t forget to to adjust the idle.

Stretch your back, loosen up your shoulders, and cover the blisters on your hand, because it’s time for a bench-test. Obviously, you’ll want to start the engine up here at home and make sure it’s running properly, before you try using it out on the water. For the initial start-up it may take a few extra pulls of the cord, because there’s no fuel in the carb right now and a drop or two of stowaway carb cleaner may remain. But hopefully the engine will be running after a few tugs, and you can take the opportunity to re-adjust the idle and fuel-air mixture screws. They’ll almost certainly need some tweaking, after the rebuild.

Now do yourself a favor, and get a quality fuel treatment designed for ethanol gas. There are several to choose from; Star Tron is my personal pick,  because I’ve used it for years and find it reliably keeps gasoline in good shape for months at a time. Biobore EB and Sta-bil are some other reputable choices. Just make sure you use one of these, or you may need to repeat this process a lot sooner than you’d like.

TIP: Every time you use your outboard, at the end of the day pull the fuel line and allow the motor to chug at idle until it runs itself out of fuel. This will prevent fuel from sitting—and deteriorating—in the carburetor, and will go a long way in helping to keep it clean.

Game On

If the engine seems to be running fine, you’re ready to put it back into service. One note of caution: you may find that the engine runs great for a short while, then begins to cough and sputter. If this happens, it probably means you loosened up a bit of gunk during the process but didn’t get completely rid of it. Now it’s finally come free, became lodged somewhere else in the carb, and is clogging up the works again. You may have to remove, disassemble, and clean the carb’s metal parts again, but you can re-use your new parts instead of getting a whole new rebuild kit.

Congratulations, you’ve just completed rebuilding an outboard engine carburetor. Now once again you can go fishing, coving, water skiing, or whatever you like. You didn’t need any fancy tools, it didn’t cost an arm and a leg, and the entire process was a whole lot simpler than most people would think. So get out there, zoom across the lake or bay, and enjoy your boat. At least, enjoy it until you hit a log or run hard aground—we’ll talk about how to change a propeller some other time.


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About the author:

Lenny Rudow

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Lenny Rudow is Senior Editor for Dominion Marine Media, including Boats.com and Yachtworld.com. With over two decades of experience in marine journalism, he has contributed to publications including Boating Magazine, Marlin Magazine, Boating World, Saltwater Sportsman, Texas Fish & Game, and many others. Lenny is a graduate of the Westlawn School of Yacht Design who has won 28 BWI and OWAA writing awards.
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