Working with the Mc43 Carburetor on Earthquake Engines
The Mc43 is a standard small-engine carburetor found on Earthquake engines used in pressure washers, portable generators, and some lawnmowers. Getting a clean diagram isn't always straightforward because Earthquake doesn't publish official diagrams the way Honda or Briggs & Stratton do. Most of what exists online comes from parts distributors who reverse-engineer the ID numbers on the carburetor body and cross-reference them. The diagram itself is fairly simple — a single-barrel downdraft design with a float chamber, a main jet, a pilot jet, and a needle valve assembly. The main components you're looking at are the float bowl at the bottom, the venturi in the center throat, the main metering jet threaded into the side of the venturi passage, the pilot jet at the bottom of the venturi feeding the idle circuit, the needle valve seated against a brass seat controlling fuel entry to the bowl, and the throttle and choke plates above. Some versions have an accelerator pump nipple on the side, but most Mc43 units are basic and don't include one. That's it. It's not complicated internally, which is both a strength and a weakness — easy to understand, easy to mess up if you lose track of which jet does what. When I needed one recently, I ended up pulling it apart blind. The carburetor was on a 7kW Earthquake generator that had been sitting with old fuel in it for about two years. Ethanol absorption does a number on these things. The pilot jet was completely blocked with varnish, the float was waterlogged, and the needle valve seat was pitted. I couldn't find a usable diagram to match the parts back together, so I traced the fuel passages myself. The main jet is a brass tube threaded into the side of the carb body — it looks like a small hex bolt from the outside but has a drilled-through center. The pilot jet sits under the venturi and is nearly invisible once assembled. You remove the bowl, lift the float pivot pin, and the main jet comes free from the top after removing the retaining clip. The pilot jet requires a small flathead screwdriver from underneath. Both are standard sizes, roughly 0.030 inches for the main and 0.020 for the pilot on a stock Mc43.
Here's something people get wrong about these carbs: the main jet size matters way more than you'd think for high-altitude operation. A stock Mc43 jetted for sea level will run rich enough to foul the spark plug at 5,000 feet. I've seen this repeatedly on generator setups used at mountain cabins. You need to swap to a smaller main jet, typically around 0.025 inches, or the engine will just bog under load and deposit black carbon on everything. The idle mixture screw on these is a brass tip that seats into the pilot passage. It's adjustable from fully seated to about three turns out. Stock setting is usually around two turns out from gently seated — don't force it. The brass tip strips easily and once it's stripped, you're looking at a new carb body or a repair kit, which are sometimes unavailable. If you're trying to source a diagram, your best bet is searching the part number stamped on the carburetor housing. It's usually laser-etched on the flat surface between the fuel inlet and the throttle shaft. Common numbers I've seen are MC43-1 or similar variations. Sites like Small Engine Parts Direct, eReplacementParts, and RepairClinic all have exploded views. The diagrams on those sites are generally accurate for the physical layout but sometimes show slightly different jet sizes depending on the engine model year. That's a known issue with these older diagrams — they aren't updated consistently across production runs. Always cross-reference the actual jet drill size if you're doing performance work rather than just reassembly. A realistic limitation with the Mc43 is availability of replacement kits. Small Engine Parts Direct carries a rebuild kit, but they're often out of stock. When they are available, it includes the needle valve, seat, float, gaskets, and O-rings. The main jet and pilot jet are usually not included and need to be sourced separately if worn. The jet sizes change over time due to wear, and a worn main jet will gradually lean the mixture as the brass bore enlarges. You won't notice it happening — the engine just gets progressively harder to tune until you take it apart and measure the jet with a drill bit gauge. This is why many people replace the entire carburetor assembly instead of rebuilding, and honestly that's sometimes the faster call unless you're doing this regularly.
The choke mechanism on most Mc43 units is a return-spring type, not automatic. You pull the choke lever, it holds open until the engine warms, then you push it in and a spring returns it to the open position. The linkage can bend if you force it, and once bent the choke plate won't seal properly at idle, causing a rich condition that's impossible to fix with mixture adjustments alone. I've had to fabricate a replacement lever from brass stock when the original cracked. Not ideal, but functional. For anyone actually doing this work, the practical takeaway is: the diagram shows the layout, but the jet sizes are what determine whether the engine runs. Start with the stock jet specs for your engine model, then adjust based on altitude and fuel condition. Keep a set of drill bits handy for checking jet wear. And don't assume every Mc43 is identical — the variations between production runs are real and documented in parts forums.
Get the Full Details
