Vintage Sears Garden Tractors
Carburetor Rebuild
One way I judge the amount of working hours an engine has had is to examine the throttle shaft. If it is worn in an oblong
shape, then you can be assured that there's lots of time on the motor. The throttle shaft here was tight. Let's take it apart and
see what's inside. The initial thoughts were not good, judging by the grunge in the throat of the carburetor. The rest wasn't too
bad when taken apart. There wasn't a lot of corrosion, but only a lot of fine, brown sediment. No big surprise there. I really
got a kick out of the milk bottle style sediment bowl fitted to this tractor. On the top of the sediment bowl assembly is written
"Zenith", which is the name of an old brand of carburetor. Everything cleaned up nicely with carburetor cleaner. No need to
ream out any passageways in this carb.
Of course the rubber gaskets were petrified over forty years of heat and gasoline exposure. I had to use an ice pick to get the
bowl gasket out. The push type drain valve on the fuel bowl is a very common source of leaks on this type of carburetor.
Again, the rubber grommet used as a gasket here was hard as a rock and took some time to get off. This gasket must be
replaced in any rebuild. In the pictures below, I am replacing the drain stem after putting on a new gasket. It's not that hard to
compress the spring by pressing down both sides with your fingers. Then you just slip the formed clip/washer on to hold it all
in place.
There are several areas to concentrate on in the main body of the carburetor. Several passages have to be completely clean for
the mixture to be right. It's not shown in the pictures, but I've removed the main nozzle from the center of the carb. That can
be difficult sometimes because of corrosion and not having a screwdriver that fits correctly. Try not to bugger up the brass
when removing the nozzle, as it may affect mixture. Carburetor cleaner and compressed air are needed to property clean the
carb. You should feel air coming out of the passageways as you blow them out. Be aware that if you remove the main nozzle
and you find it is the old style, you will have to replace it with a service nozzle. The small hole in the nozzle is drilled once it is
screwed into the carb body. There is no way to line it up correctly after you remove it. The service nozzle can be identified by
the groove cut into the threads. While no longer available from Tecumseh or Walbro, you can still get one here:
Replacement Nozzle.
This carburetor still had the original shut-off needle and seat in it. The rebuild kits come with updated parts that are
intended to keep the carburetor from flooding. There's a rubber seat that has to be installed, a spring on the fuel flow needle
that has to engage the tang of the float and a spring that goes on the pivot pin of the float. All three of these improvements
make it more difficult to put it all back together. Make sure the rubber seat is completely bottomed out in the needle valve
assembly. I used a drill to push it all the way in. Check the float level with the new seat assembly. I had to adjust mine. The
hardest part is putting the float assembly, with springs and needle valve, on with only two hands. It WILL take more than
one attempt. Also, the rubber gasket for the bowl will need to be stretched out to fit in the groove in the carb body.
Don't forget the fiber washer between the bowl and bottom of the main nozzle. Also, the main needle assembly has a fiber
washer for it too. There was a thick washer and thin washer. The directions didn't say which one went where, so I put the thin
one under the bowl and the thick one on the main needle. I don't know if that's right, but it worked for me. Gotta love that
milk bottle sediment bowl!
Grunge in throat of carb
Not bad inside
Cleaned parts
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© 2007 VSGT