How do I Adjust a Carburetor Float on a Marvel-Schebler?by Chris Stevenson
Marvel-Schebler carburetors have been manufactured for many tractors and other industrial engines. Their simplistic design and heavy construction gives them many years of trouble-free service. The Marvel-Scheber carburetor consists of an idle circuit, float system with metering needle, power valve, venturi and choke function. These components work in conjunction with each other to delivery a precise, metered amount of fuel to the engine system. Fuel atomizes in the carburetor throat and enters the engine cylinders for combustion. A float bowl that contains a hinged float, controls the amount of fuel that enters the carburetor. Adjusting the float to the proper height insures proper fuel delivery, or fuel starvation or flooding results.
Position the vehicle or engine for easy access to the top of the carburetor. Unclasp the snaps, and pull back the engine cowl if so equipped on a tractor or other farm vehicle. Use a screwdriver to remove the case side or top covering if working on a generator.
Use a socket to remove the negative battery cable. Turn off the main fuel supply valve to the carburetor. Use a socket or screwdriver to remove the air cleaner assembly housing, including any draft tube or ventilation tube to the air cleaner cowl.
Use a pair of needle-nose pliers to remove the retaining pins that hold the two linkage rods on the carburetor. Pull the throttle cable socket off the linkage ball on the cam. Don't lose the small retaining pins, or cotter pins.
Use a fuel line wrench to loosen and remove the fuel line from from the carburetor. Place a rag underneath the fuel line to catch drippings. Pull the heat tube free if it has one attached to the carburetor.
Use a socket to remove the two carburetor base bolts. Gently pry the carburetor free from the intake manifold and take it to a work bench. Use a large flat-head screwdriver to remove the four air horn (top case plate) screws, and separate the two halves of the carburetor body.
Flip the the air horn over and examine the float. Gently tap it to make sure it has no fuel inside it. You will have to replace the float if fuel has entered inside it. Make note of the pivot rod the float sits on and the gap underneath the bottom of the float and the case plate.
Place a 1/8 inch drill bit underneath the float to gauge the proper float height. The float should not swivel upward upon pushing the drill bit underneath it, nor should it have a gap wider than the diameter of the drill bit. To adjust the float height, use needle-nose pliers to bend the small tang arm that attaches to the float and the pivot assembly. Bend the tang either up or down.
Use a float gauge (if you prefer this method) to eyeball the distance by placing the gauge upright against the float and looking for the 1/8-inch mark. Turn the air horn over and place it back on the carburetor base. Insert the screws and tighten them with a screwdriver. Place the carburetor back on the intake manifold and tighten the mounting bolts with a socket. Snap the throttle cable ball back onto its socket.
Replace the heat tube in its socket. Reconnect the linkages arms, and secure the retaining clips or cotter pins. Thread the fuel line into the carburetor by hand and tighten it with a fuel line wrench. Replace the air cleaner assembly, and tighten the bolts with a socket or screwdriver. Replace the draft tube if removed. Reconnect the negative battery cable and tighten it with a socket.
- Some Marvel-Schebler carburetors have twin floats for the same bowl. Bend each individual tang on each float to achieve the proper gap on both sides.
Things You'll Need
- Carburetor service manual
- Socket set
- Ratchet wrench
- Fuel line wrench
- 1/8-inch drill bit
- Float gauge ruler
- Needle nose pliers
Chris Stevenson has been writing since 1988. His automotive vocation has spanned more than 35 years and he authored the auto repair manual "Auto Repair Shams and Scams" in 1990. Stevenson holds a P.D.S Toyota certificate, ASE brake certification, Clean Air Act certification and a California smog license.