| rn How-To: Carburetor Rebuild
rn By: Terry (aka: T-Mo on RedSquare) rn DOWNLOAD THE PDF VERSION OF THIS MANUAL - CLICK HERE rn
rn Since some of the new members of RedSquare ( http://www.WheelHorseForum.com ) may be unfamiliar with rebuilding a carburetor, I thought I would document the process as I went through one today.
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rn First, disconnect the battery to eliminate any chance of creating sparks. Remove the choke and throttle linkages. Close the fuel shutoff valve. Remove the fuel line from the carburetor. Hold a small can (an empty tuna fish can is the perfect size) under the carburetor to catch any gas that is released during dis-assembly. Loosen and remove the two bolts holding the carburetor to the engine. Keep the can under the carburetor while you carry it to the workbench.
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rn Next, remove the bolt holding the bowl onto the carburetor (gas will probably come out when the bowl seal is broken so hold the carburetor over the can while doing this). It may also be necessary to tap on the bowl lightly with a rubber mallet after removing the bolt. Once the bowl is removed, slide the float pivot pin out and remove the float and needle assembly. Pry the old gaskets out and remove the old valve seat with a 3/8" nut driver.
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rn If the tractor was running before carburetor removal, take note of the position of the Idle (LO) and Main (HI) mixture screws. I usually screw them in until they gently bottom, counting the number of turns. I write the numbers on the cardboard I use to keep the workbench clean. After doing these steps you will arrive at something which looks like Figure 1.
rn  rn Figure 1 rn The next step, cleaning, you will need a 1-gallon can of Carburetor & Parts Cleaner in which to soak the carburetor. A spray can of the fast-evaporating carburetor cleaner is also handy during this process step. rn  rn Figure 2 rn Pre-clean all of the large chunks of dirt and grime from the outside surfaces and then put all of the carburetor parts in the basket except for the float (as it is difficult to completely submerge it). Let them soak for about half an hour. Clean the float with the spray can of cleaner. If the Float looks questionable or you can hear gas sloshing around inside of it, replace the Float. Lately I've been preemptively replacing floats because I don't like taking these things apart more times than I have to. rn
rn After 30 minutes or so in the carburetor cleaner, some scrubbing with an old toothbrush, and rinsing the parts, the carburetor should look something like this:
rn  rn Figure 3 rn The can of carburetor cleaner works wonders. Both the throttle and choke were stuck on this carburetor, and after soaking, both were free. I didn't bother leaving it in there until all the paint fell off as; (1) this is going on a work tractor and not a restoration tractor, and (2) it's eating the carburetor metal while it's in the solution, so I only leave parts in there only as long as is necessary. rn
rn Note in Figure 3 that I have removed the Butterfly Valve and the Throttle Shaft. I have done this because this carburetor needed to have a new Throttle Shaft Bushing installed in order to correct excessive play in the Throttle Shaft. If the Butterfly Valve is to be removed, extreme care and patience are necessary not to twist off the heads of the brass screws. When the brass screws are installed, the tail ends of the screws are peened over they do not vibrate out and get sucked into the engine. This the screws very difficult to remove.
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rn To correctly remove the brass screws, loosen and tighten each screw 1/4 turn at a time, and loosen/tighten them several times 1/4 turn at a time, until they can be completely removed. After ensuring that everything is clean and all passages are open, install the throttle shaft bushing if necessary by using a 1/4" bolt as a guide, as shown. Install so that the top of the Bushing is flush with the top of the carburetor body.
rn  rn Figure 4 rn rn  rn Figure 5 rn Next, reinstall the throttle shaft and butterfly valve. DO NOT attempt to re-use the brass screws you removed, as they'll just twist off when you try to reinstall them (don't ask how I know this). Pick up some new screws (I think they're #3-48) and lock-washers, as well as some blue Lock-Tite. Install the screws with lock-washers and Lock-Tite. rn  rn Figure 6 rn The rest of the carburetor is assembled next. Open up your carburetor kit (and new float, if that was necessary) and make sure you have all the parts. The small red gasket goes on the bowl bolt, and the black [Kohler kit] or white [some aftermarket kits] one goes on the seat. rn  rn Figure 7 rn Make sure the main needle jet passages are not clogged. There are several sets of holes in the needle, and after soaking in the carburetor cleaner; all of them should be open and clear. To check if the passages are clear, stick the pointy end of the needle in your mouth and blow. Air should be coming out of the two upper sets of holes. If not, it's not clean enough. If it's clear, reinstall the Main (HI) and Idle (LO) needles in their respective locations. I usually set the Main Jet Needle 2-1/4 turns out from seated, and the Idle Jet Needle 1-3/4 as a starting point. rn
rn Install the new valve seat, valve, and float, and check and adjust the float level. The specific Engine Service Manual describes two measurements for this step (for the particular carburetor installed on your engine), but I normally set them by eye. When the Carburetor Body is turned up-side down, the float should be parallel to the carburetor body, or slightly “up” (which is “down” when the carburetor is in its installed position) as shown “slightly up” in Figure 8. To adjust the Float height, bend the tab on the float to achieve the correct relative position.
rn  rn Figure 8 rn After the float level has been set, remove the float again, and then put in the gasket that looks like a square O-ring. This is a three-ring circus if you are using an aftermarket gasket set, as it has to be stretched to fit and likes to fall out. After you get it in, make sure it isn't twisted. rn  rn Figure 9 rn Install the baffle (splash) gasket over the top of the square gasket as shown in Figure 10 and re-install the Float. rn  rn Figure 10 rn Some aftermarket kits come with this POS float pivot pin that is knurled on one end. If yours has this, use the old pin that was originally installed in the carburetor. Re-install the bowl, being careful not to disturb the position of the two gaskets. The carburetor is now ready to reinstall on the tractor. rn | rn 
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