If you've been yanking on that starter cord for twenty minutes and getting nothing but a sore shoulder, your subaru ex27 carburetor is likely the culprit. It's a frustrating experience, especially when you have a big project lined up and your pressure washer or generator decides it's not in the mood to work. These 9HP overhead cam engines are actually fantastic pieces of machinery, but like any small engine, they live and die by the quality of their fuel system.
Most of the time, the engine isn't actually "broken." It's just that the tiny, intricate passages inside the carburetor have been gummed up by old gasoline. We've all been there—leaving fuel in the tank over the winter and hoping for the best in the spring. Usually, the "best" doesn't happen. Let's dig into what makes this specific carburetor tick and how you can get your equipment back in action without losing your mind.
Signs Your Carburetor Is Acting Up
Before you go tearing things apart, it's worth double-checking the symptoms. A bad subaru ex27 carburetor usually lets you know it's unhappy in a few specific ways. The most common is the "surge." You know that sound—the engine revs up, then almost dies, then revs up again in a rhythmic, annoying cycle. This is often called "hunting," and it's a classic sign that the engine is starving for fuel because of a partial clog.
Another big red flag is when the engine will only run with the choke partially on. If you flip the choke to "run" and the engine immediately dies, you've got a lean condition. Basically, the main jet is restricted, and the engine needs the extra suction from the choke just to pull enough gas to stay alive. And then, of course, there's the total failure: you've got spark, you've got compression, but the spark plug stays dry as a bone no matter how many times you pull the cord.
Why Do These Carbs Get So Clogged?
The real enemy here isn't Subaru's engineering; it's modern pump gas. Most fuel you buy today contains about 10% ethanol. Ethanol is great for some things, but it's terrible for small carburetors. It's hygroscopic, which is just a fancy way of saying it attracts water. Over time, that water and ethanol mix creates a sort of corrosive "snot" or crusty white oxidation inside the bowl of your subaru ex27 carburetor.
Because the passages inside this carb are incredibly small—some are barely wider than a human hair—even a tiny flake of debris can shut the whole thing down. If you leave your machine sitting for more than a month without a fuel stabilizer, you're basically inviting these problems to dinner.
Cleaning vs. Replacing: Which Is Better?
This is the age-old debate for anyone working on small engines. On one hand, you can buy a generic aftermarket subaru ex27 carburetor online for remarkably little money. Sometimes it's cheaper to buy a brand-new one than it is to buy a can of high-quality carb cleaner and a gasket kit.
However, there's a catch. The original Mikuni or Robin/Subaru carbs are built to very high tolerances. The cheap knock-offs can be hit or miss. Sometimes they work perfectly right out of the box; other times, the casting is rough, the float height is wrong, or the jets aren't sized quite right. If you have the patience, cleaning the original carb is usually the better long-term move. But if you're in a rush and just need the machine to run for a weekend project, a quick replacement might be your best bet.
How to Remove the Carburetor Without the Headache
Taking the subaru ex27 carburetor off the engine isn't too difficult, but there are a few "gotchas" to watch out for. You'll usually start by removing the air cleaner assembly. Once that's out of the way, you'll see the carb sitting there, held on by two long studs.
Before you pull it off, take a picture of the linkage. The way the governor spring and the throttle rod hook into the top of the carb can be a bit of a puzzle if you don't have a reference. It's incredibly easy to forget which hole the tiny spring goes into. Once the linkage is disconnected, slide the carb off the studs. Be careful with the gaskets! The EX27 uses a specific sequence of gaskets and a plastic heat spacer. If you rip one or put them back in the wrong order, you'll end up with an air leak, and the engine will never run right.
Tips for a Deep Clean
If you decide to go the cleaning route, you need to do more than just spray the outside with some cleaner. You have to get into the "guts." Drop the bowl by removing the bolt at the bottom. Be careful—this is where the gas will spill out. If the inside of the bowl looks like a science experiment gone wrong, you've found your problem.
The most important part to clean on the subaru ex27 carburetor is the main jet. It's located inside the center column that the bowl bolt screws into. You'll need a flathead screwdriver that fits the slot perfectly; if you strip the brass jet, you're in trouble. Once it's out, make sure you can see daylight through the center hole. I often use a single strand of wire from a wire brush or a very thin guitar string to gently poke out any stubborn deposits. Just don't go crazy and enlarge the hole, or you'll make the engine run too rich.
Don't forget the pilot jet! On many of these models, it's tucked under the idle screw on the top of the carb. This tiny little guy is almost always the reason for the "surging" idle. If that passage is blocked, the engine can't get fuel at low RPMs.
Reassembly and the Gasket Maze
When you're putting the subaru ex27 carburetor back on, pay close attention to the gaskets. Usually, it goes: engine block, gasket, plastic spacer, gasket, carburetor, gasket, air filter housing. If you miss one, the engine will suck in "unmetered air." This leans out the mixture and causes the engine to rev uncontrollably or die under load.
Also, make sure the fuel line is in good shape. If it feels crunchy or has cracks, replace it now. A tiny piece of rubber flaking off the inside of an old fuel line will go straight into your freshly cleaned carb and clog it up all over again. It's also a great time to install an inexpensive inline fuel filter if your machine doesn't have one. It's cheap insurance.
Tuning for Peak Performance
Once everything is back together and the engine is (hopefully) humming along, you might need to make some minor adjustments. Most modern subaru ex27 carburetor versions don't have a lot of adjustable needles because of emissions regulations, but you can usually adjust the idle speed.
If the engine is vibrating like crazy, the idle might be too low. If it's trying to "walk" across the driveway while it's supposed to be sitting still, the idle is likely too high. Find that sweet spot where it stays running smoothly without sounding like it's about to take off. If you're still getting a bit of a surge, try adding a little bit of a high-quality fuel system cleaner to the tank—sometimes it just needs a few minutes of hot running to clear out the last bit of residue.
Preventing Future Issues
The best way to deal with a subaru ex27 carburetor problem is to never have one in the first place. It sounds simple, but very few people actually do it. If you're done using the machine for the season, turn off the fuel valve and let the engine run until it dies. This clears the fuel out of the carburetor bowl so it can't turn into varnish over the winter.
Alternatively, use ethanol-free gas if you can find it in your area. It's more expensive, but it lasts much longer and doesn't eat away at the internal components of the fuel system. If you have to use regular pump gas, always add a stabilizer. It's a lot cheaper to spend five dollars on a bottle of stabilizer than it is to spend fifty dollars and three hours of your Saturday fixing a clogged carb.
Final Thoughts
Dealing with a subaru ex27 carburetor might feel intimidating if you aren't a mechanic, but it's actually a very logical system. It's just about fuel, air, and keeping things clean. Whether you choose to spend an hour scrubbing the old one or just swap it out for a fresh unit, the satisfaction of hearing that engine roar back to life on the first pull is worth the effort. Just remember to take your time, keep track of those tiny springs, and maybe keep the ethanol-free gas nearby for the next time you fill up. Your back (and your starter cord) will thank you.