I was having issues with the original carb on the Trials bike. Yes, I can get rebuild kits, but they are damn near as much as a new carb. So I decided to splurge and picked up a 19mm Keihn for something like $29. I also got a new air filter for it, some fuel like, a couple small filters, and a on/off valve.
But the hard part was making an intake manifold to mount up the carb. The original is a downdraft style, while all the newer small carbs are sidedraft. Luckily I had some old washers, pipe, and a few old pipe fittings laying around. The pipe fittings proved a great way to make the 90-degree bend, and are rather hefty. After an hour or so of cutting, drilling, and welding, I make a rather ugly intake manifold that luckily is masked by some black paint.
The entire thing assembly mounted up quite nicely:
I combined both the normal and reserve fuel lines from the later model C102 fuel tank to a "Y" fitting, then to a on/off valve, then a small fuel filter. This way I don't have to spill fuel everytime I mess with the carb or filter:
The best part is, it fired right up and seems to run great. I have the mixture screw set 1 turn out, and the idle screw maintains a perfect idle speed. It runs much cleaner through the range, and seems to have more poke. Maybe 4.6hp instead of 4.5hp.