Rebuilding a carburetor on an old Toro 2-stroke commercial mower

baymee(LehighValleyPA)June 30, 2013

This mower was dropped off with two other commercial mowers. None had run for years and the other two were junked. I kept this one because it has such a good reputation. It’s been under my deck for about two years. The model number is Toro 20680, Serial 4008211. The first step of this project is to look at the carburetor behind the air filter housing.

I’m not surprised; mice like nice things too!

Mice don’t leave any stone unturned when making a nest. This is a good picture of the linkage and its position.

The piston and one ring is showing behind the carburetor. There is very little scuffing and everything looks good so far.

The fuel bowl still held a half-bowl of old fuel. Everything is badly varnished.

The main jet is blocked solid with varnish. It is located just below the threads, where the bolt that holds on the bowl, would be.

Looking into the emulsion tube, I can see that there is no removable jet inside there. In many carburetors, there is a long jet screwed into there and you’d be able to see a cut to use a flat screwdriver to remove it. In this case, it’s just a tube.

Shown here are the float, needle, pin and spacer between the carburetor and the cylinder. Note the flat spot on the pin. When removing the pin to free the float, the side of the pin with the flat is like a nail head. Push on the side opposite the flat spot to remove the pin. Install in like manner. The pin may not come out easily and the carburetor might have to be put in a vise and a hammer and punch used to free the pin

Remove the jet on top of the carb with a flat head screwdriver.

Another view of the proper installation of the linkage, with the choke mechanism in the foreground.

Both jets are now removed for cleaning. The jet on the right has three holes drilled around the circumference and a very small hole in the end, facing up.

The main jet has been cleaned. It is a rather large hole and easy to clean out with a wire and carb cleaner. Look through it to ensure that it’s free of varnish.

The metering jet orifice is so small that only one strand of 16 gauge stranded wire will fit through it.

On this flange, which is on the outside, air filter side, of the motor, there are three holes. Use carburetor cleaner and compressed air to clean them out. Be careful: The orifices are small and carb cleaner can spray back at your face. Blowing compressed air into them will force the carb cleaner out at another port in the carburetor. This verifies that the passageway is clean and is also a warning that you should expect carb cleaner to exit anywhere. Wear safety glasses when doing this.

On the left side, below the upper hole with no jet, note the lower hole has a jet pressed into it. This leads to the center of the carb and exits at the threaded area where the bowl securing bolt would screw into. This MUST be clean or the carburetor will not work. If carb cleaner is sprayed into that hole, compressed air will force it out as a mist in the bolt’s threaded area. If no carb cleaner sprays out, the passageway is blocked and must be cleaned, or the carb will not work. The same is true for Tecumseh carbs.

The tube on the left side is for the overflow, in case the float would stick open.

The carburetor is now clean and ready for re-assembly. Do not overtighten the two jets. Just make them snug. It usually isn’t necessary to replace the O ring on these carbs, but the two gaskets are another matter. You want to get a good seal, so replace if needed.

The top jet is cleaned and re-installed. It looks as though a hole is drilled into the jet from the top, but it isn’t. The best I can determine, the carb’s number is 90612, E373.

There is only one Welch plug installed in this carb. I only remove them if I can’t get the passageways cleaned out by other means. I did not remove the plug.

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Put everything back together. Possible problem. No spark. Hopefully just an adjustment of the kill switch.

    Bookmark   June 30, 2013 at 4:13PM
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Found the problem. It's related to the flywheel brake switch. Starts and runs great!

    Bookmark   July 1, 2013 at 7:43PM
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Good work! Those engines must be nearly indestructible. The previous owner obviously did not use my special 2-cycle brew; whatever oil mix + 2 oz/gal MMO + Sta-Bil.

    Bookmark   July 3, 2013 at 8:43PM
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