Understanding the Carburetor on a Troy-Bilt TB160
The TB160 is a two-cycle trimmer/edger combo that uses a very basic side-draft carburetor. It's the kind of carb you see on thousands of cheap small engines — not precision engineering, just a plastic body, a couple of rubber diaphragms, and some small metal passages. When it gets dirty or the diaphragms harden, the machine runs poorly or won't start at all. Most people who own one end up pulling it apart and trying to make sense of what they're looking at. If you need a reference, search for "Troy Bilt Tb160 Carburetor Diagram" and you'll find several versions floating around on parts sites and forums. The problem is most of them are low-resolution scans pulled from a parts manual, and some of the labels don't match the actual carb you have on your machine. Troy-Bilt changed suppliers over the years, so the carburetor on a 2005 TB160 might look different from the one on a 2012 model.
Troy Bilt Tb160 Carburetor Diagram
Here's what you're actually looking at when the carb is taken apart. The main body is usually a two-piece plastic housing held together with two or three screws. Inside you'll find: Fuel inlet side: This is where the fuel line connects. There's a small brass filter screen pressed into the inlet port. A rubber fuel line runs from the tank to this point. If that screen is clogged with old fuel residue, the engine will starve for gas at high RPM even if the tank is full. Diaphragm assembly: This is the critical part. There are two diaphragms — one is the fuel pump diaphragm that moves fuel from the tank, and the other is the metering diaphragm that controls how much fuel gets into the mixing chamber. They're separated by a flexible divider. Both are made of coated fabric, usually neoprene or a similar material. Over time, especially if ethanol-blended fuel has been sitting in the carb, these become brittle and lose their ability to flex. That's the number one reason a TB160 that was running fine last season suddenly won't start this one.
Primer bulb: The clear or colored rubber bulb on top of the carb. It's connected by a small passage to the fuel chamber. When you press it, it draws fuel into the carb to help with cold starts. On these carbs, the primer bulb sometimes cracks along the seam after a few years. A cracked bulb means no prime, which means no cold start. I replaced one by carefully peeling the old bulb off the housing and gluing a new one in place with thin cyanoacrylate. It sounds hacky but it works fine. Buying a replacement carb with a new primer bulb usually costs more than the whole used carb. Jets and passageways: The main jet is a tiny brass tube pressed into the carb body. The idle jet is smaller and feeds fuel at low throttle openings. Both passages are maybe 0.5 to 1 millimeter in diameter. A piece of dried fuel deposit the size of a grain of sand will block them completely. Cleaning these with compressed air and a strand of copper wire from inside an electrical wire works better than anything else. Carb cleaner spray helps but it doesn't dissolve baked-on ethanol residue the way people expect it to. Throttle linkage: A small metal arm connects the carb to the control cable. There's a spring pulling the throttle toward idle. The idle speed is adjusted by a screw that presses against the throttle arm. Turn it in and the idle goes up. Turn it out and the idle goes down. There's usually a lock nut too, though on these cheap carbs the lock nut is often missing or stripped already.
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Gaskets: The carb mounts to the engine cylinder through a gasket. This gasket is usually paper or fiber and it compresses to seal the intake port. If you reuse an old compressed gasket, air will leak in around it. An air leak right after the carb means a lean condition — the engine runs hot, backfires, and may seize if you push it hard enough. Always replace that gasket. They cost about thirty cents each on eBay. I had a TB160 last spring where the engine would start and run for about ten seconds then die. Checked everything — fresh fuel, new spark plug, clean air filter, clear fuel line. Nothing. Finally pulled the carb apart and found the metering diaphragm was split down the middle. Not visible unless you hold it up to the light and flex it slowly. The split was maybe two millimeters long. The fuel pump diaphragm looked fine. Replaced both diaphragms as a set along with the gasket kit and it ran perfectly after that. The whole diagnosis took about forty-five minutes because I had already spent two weeks convincing myself it was something else.
How to Approach This Carburetor in Practice
Start with the simplest stuff before tearing the carb apart. Make sure the fuel in the tank isn't older than about six months. Ethanol absorbs water from the air and breaks down, turning into a varnish that coats every passage in the carb. Fresh fuel and a fuel stabilizer will solve more TB160 problems than any carb rebuild kit ever will. If the fuel is fresh and it still won't run, check the primer bulb. Press it firmly. It should resist and spring back. If it feels soft or does nothing, there's either a crack in the bulb, a disconnected passage, or a failed diaphragm. The fuel line from the tank to the carb should also be checked. These lines get brittle and develop internal collapses that restrict flow. Replace them with standard small-engine fuel line — not vacuum hose, not garden hose. Something rated for gasoline. When you do pull the carb apart, take photos at each step. These carbs have maybe eight fasteners and three to four small springs. The springs can fly off and disappear if you're not careful. I keep a magnetic parts tray on my workbench for this exact reason. It's saved me more than once.
The diaphragm kit is the part that matters most. Don't bother cleaning the old diaphragms. They're cheap — usually ten to fifteen dollars for a complete kit that includes both diaphragms, all gaskets, and sometimes a new primer bulb. Just replace them all at once. The metal parts inside the carb body — the jets, the throttle plate — usually last for years unless the carb has been physically damaged. The throttle plate is a flat piece of metal that pivots on a pin. Make sure it moves freely and snaps shut when you release the throttle cable. Reassembly tip: when you put the carb back on the engine, don't overtighten the mounting screws. These plastic housings crack easily. Snug is enough. Overtightening warps the housing and creates the kind of air leak that makes diagnosing the problem take another two hours. After reassembly, the idle adjustment screw needs to be set. Start with it threaded in about one and a half turns from fully seated, then adjust while the engine is running. The goal is a steady idle where the trimmer head doesn't spin but the engine doesn't stall either. If the engine runs fine at idle but surges or dies under load, you're either still getting an air leak or the main jet passage isn't fully clear.
When a Rebuild Won't Fix It
There are cases where the carb itself is damaged beyond a simple rebuild. I've seen a few where the throttle shaft bore is worn — the shaft wobbles slightly in its hole. This creates an unmetered air leak that no gasket or seal can fix. The only real fix is to replace the entire carburetor assembly or the carb body. Aftermarket copies are available for around twenty to thirty dollars and they're usually adequate for the application. Another failure mode is a cracked carb body. Hairline cracks near the mounting flange or around the diaphragm chamber are common in older units. You won't see them until you clean the part and hold it to light. Epoxy or superglue might hold for a short time but the heat cycling from the engine will eventually open the crack again. Replacement is the only permanent fix. If your TB160 has been sitting with bad fuel in it for a year or more, the internal passages may be so coated with varnish that even a rebuild kit won't restore proper function. In that case, swapping to a replacement carb is faster than trying to clean everything out. A new carb takes about twenty minutes to install and costs less than the time you'd spend disassembling, soaking, and rebuilding a fossilized one.
The best source for a clean diagram showing the exploded parts view is the Troy-Bilt parts diagram for your specific model year. You can find it on sites like eBay, Amazon, or smallengineshop.com by entering your TB160 model number and serial number. The serial number matters because production changed mid-year. The carburetor portion of the diagram will show you the exact part numbers for your carb so you can order the right rebuild kit instead of guessing.
