We all like to see old engines restored to the original condition, just as they were when they were new. Sometimes, however, parts are missing and cannot be located. A choice must be made to forget the engine, or to use non-standard parts, or even homemade parts. This was the case with a Jumbo engine (Nelson Bros.) which I was able to obtain recently. I only obtained the basic castings. There was no valve mechanism, no governor latch, no ignition system, and worst of all no mixer valve, or carburetor as some call it. I was able to make all of these parts, and now have the engine running.
Most of my 'engine nut' buddies had agreed that the mixer would be the most difficult to make without the use of a machine shop. Actually it turned out to be quite simple using only hand tools, a gas welder, a drill, a hacksaw, and file. The materials required are available at any hardware store.
This mixer works fine on my engine, and I believe it will work on any small (1 to 2 HP) hit-and-miss engine. In the hope it may help someone else save an old engine, I have made some pictures and sketches of how the mixer was made.
Some things to keep in mind while looking at the sketches. The use of 1/8 inch pipe couplings (which are about 1/2 inch actual outside dia.) across the one inch main body tube forms a kind of venturi which will siphon fuel from the tank without the choke closed. This is a necessary part of the construction. On an angle mixer the venturi effect can also be controlled by how close the back corner of the mixer body is cut off. If you want the engine to run well at slow speed, then make the cut about 1/4 inch or less from the cross couplings. If the engine is to run fast, and make a lot of power, then increase the distance. Keep in mind if the distance is larger, then the air flow through the mixer at low speed may not be enough to lift fuel from the tank. Most of us like to see these old engines run slow, and often we don't pull any load at all, so I cut my mixer a bit less than 1/4 inch to produce a strong venturi effect, and give good low-speed performance.
The following is a 12-step procedure to make a mixer (see the diagrams in the Image Gallery for a visual step-by-step):
1. Cut 1-inch ID electrical conduit at 45 degrees.
2. Notch cut ends with a rat-tail file.
3. Weld to form an elbow. Run a drill through the hole to smooth it.
4. Weld two 1/8-inch pipe couplings together for necessary length. Grind or file the weld smooth. Drill a 1/8-inch hole at center one side only.
5. Saw off the corner of the ell at 45 degrees, about 1/4-inch from the hole.
6. Weld or braze a nut to the center of a washer of the size to just cover the hole produced by cutting the corner in step No. 5.
7. Weld or braze the washer and nut to cover the hole in the back corner of the ell. Use care to keep it on center.
8. Use a 1/4-inch cap screw about 1 inch long. Chuck in a drill and spin it against a file or grinder to form a needle. The point should be about 3/8-inch long.
9. File or ream the hole until the 1/8-inch pipe couplings will just slip through.
10. Slip the couplings in place and turn the hole to face the pointed screw. Screw the point into the hole in the coupling snugly. This will hold the coupling in the correct position while the ends are brazed to the elbow.
11. Weld a flange or whatever is required to fit the engine. Also a choke plate. It is a good idea to cover the lower front air horn about 1/4-inch up to avoid fuel drip.
12. Screw an angle valve in one side of the coupling and plug the other side. Connect to the fuel tank through a check valve. The tank should be slightly below the mixer. The needle must be adjusted to the engine.