The Yamaha Champ is a 2 speed automatic shaft driven, 2 stroke, 49cc scooter made from 1980 to 1981. There are two model numbers for the bike The LC50G for the 1980 year and the LC50H for the 1981 production year. This bike is also called a Yamaha Bop 2 in Europe and a Yamaha Malic in Japan. It has a number of “advanced” features that make is a bit of a unicorn among scooters of the era. Another thing to note is that this bike uses a 6 volt electric system.
The petcock used vacuum from the intake manifold to allow the flow of fuel automatically. This system is all mechanical. Yamaha used this feature on a few other bikes such as the Razz and Riva. There is a rubber gasket in the petcock that separates the vacuum pressure from the fuel. The vacuum pressure from the intake opens the rubber gasket and allows fuel to gravity feed past it. The gasket returns to its origional shape onn its own when the bike is shut off stopping fuel flow. The rubber gaskets in these bikes are now over 30 years old and may be cracked or leaking.
Auto Choke and Carb
There is a bimetal valve on the head that uses heat from the engine to automatically switch from the choke circuit to the regular running circuit in the carburetor. This is done through a number of hoses, a check valve and splitters and is all mechanical. (Note - they no longer make the bimetal valve). These valves are old and prone to failure and if yours fails they are not manufactured anymore. You may be able to source a used one on Ebay or a forum buy and sell. But you can also upgrade your carburetor as an alternative. You would then need to disconnect the bimetal valve and the mass of vacuum lines running to the old carburetor and run a single line from the engine head to the vacuum line on the auto petcock. The QT50 carburetor does work on the LC50 and fits on the intake manifold. You will need to take the QT50 right hand controls to operate the cable choke.
Going big bore and modding
The PW MJ and QT 50 big bore kits will fit this machine as will the 60cc Yamaha Yzinger top end. There are a number of different aftermarket brands ranging from the cheap end like Niche Industries to the more expensive like the Malossi Polini Kits. The more expensive kits are bigger and offer better cooling. Before selecting a kit make sure you do your research because the spark plug can have interference on some kits. When you swap the cylinder jug you are going to lose the mounting point for the bimetal valve which controls the auto choke circuit for the carburetor. This means you will have to do a carburetor upgrade/conversion as well. The DellOrto PHBG carburetor comes in 15 17 and 21 mm sizes with the optional choke kit installed you do not need to swap your hand controls for the QT as the chock is controlled directly on the carburetor. If you do a carburetor upgrade you may need to install a bigger intake manifold, you will most likely lose the vacuum line. The vacuum pressure is split and sent to the bi-metal valve and the auto petcock. If you choose to delete the vacuum line you will have to find a replacement carburetor and fuel petcock. If you do a big bore kit but keep the stock intake and use a QT50 carburetor for example, you can simply run a vacuum line from the intake to the fuel petcock.
This bike had a low production run for only 2 years and because of this the one off parts are going to be almost impossible to find such as fenders crankshafts etc.. The best place I have found is Ebay, forum buy and sells. If you look over seas for parts remember this bike was also called the Malic or Bop 2 in Japan they commonly use Yahoo marketplace to sell used items. Luckily though, this bike does share a large number of parts with other bikes. Compatibility can be found here.
I have been researching Rim options and 12 Volt conversions I have been gathering the specs together not listed in the manual.
Front Rim / Wheel 10mm center shaft (AxleShaft) 10 inch rim x 2.15 inch width 10 x 3.5 tire
Rear Rim / Wheel 10 inch rim x 2.15 inch width 16 Spline centershaft 10 x 3.5 tire
LC/QT 50 Stator Mounting Hole Spacing - 95 MM Frame Diameter - 82 MM Drive Shaft Opening - 19.5 MM
LC/QT 50 Flywheel Outer Diameter - 113.6MM Inner Diameter (Magnets) - 84.72 MM Depth - 40.89 MM Shaft opening (Tapered) - 13.47MM - 16.88 MM