The carburetor fitted to the Jet Board engine is a Tecumseh diaphragm carb that was also fitted to a variety of Tecumseh engines. It has an eight petal reed valve intake into the main crank case. The diaphragm system works off the crankcase pressure and inflates and deflates a small balloon to pump gasoline into the venturi. There is no float bowl like a typical two stroke engine. There are very few markings on the carb but below are two shots with the markings shown.

Below is a shot of the carb when it was pulled off the motor (before cleaning).

We purchased a rebuild kit (Part# 631893) and set about cleaning and restoring the carb. There were a few unique things about this carb that I was unfamiliar with. To meter the gasoline coming into the carb body, there is a flap system directly underneath the intake. These flaps work as valves depending on whether there is a vacuum under the diaphragm. The shot below shows the flaps with the intake stub faceplate removed.

There is a small red rubber balloon that is fitted into the carb body. This balloon expands when the crankcase is pressurized as the piston comes down through the bore. As the pressure in the crankcase turns to a vacuum as the piston rises, the balloon deflates. This action works as a fuel pump and is so effective the gas tank valve can be lower than the carb position. The shot below shows the balloon being inserted in the correct hole. This balloon is also part of the rebuild kit.

The final parts we replaced were the diaphragm and the needle, jet, and spring assembly. The main brass jet is a very close fit to the carb body. We had to slightly grind down the face of a socket to remove the jet. Once removed the new assemble can be installed as shown below.

The reed valve had fiber petals on one side and stainless steel ones on the other. I don't know why that was, but we kept it as we found it. Below are two shots of the reed cage before cleaning. You can see the small hole for the crankcase pressure to fill the balloon fuel pump system shown with a red arrow.

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