Motorcycle Repair: other carbs, camshaft timing, honda cm

Question
hi once again i have a 1982 honda cm 400tc made for the german market which after some research have discovered these bikes had different carbs from the american ones the carbs were vb31d can you tellme if the carbs from an american model will work ok i am finding it hard to get spares jets e.t.c for my bike

Answer
Fergus, I don't have any way to access German-market parts lists, however due to their restrictions dating back into the 1960s and beyond, Germany often insists on various ways to control either noise and/or engine output.

Engine fuel calibration is a function of airflow through the entire powerplant from air intake to the tip of the exhaust pipe. If the air box is restricted for reduced airflow/noise then the air/fuel mixtures will be different than that for a free-flowing system. Same thing applies for the exhaust system, if they built in some extra restrictions there, as well. They can change the camshaft timing, compression, intake port/valve sizes, etc. to achieve those goals.

Physically, the engines are all the same dimensions, so I imagine that there would be no issues with actually bolting a US carb set onto your bike. You might want to invest in some jet reamers, so you can make your own jet sizes with what you have, as an option.

Any changes you make to the bike's whole powerplant design will probably require re-jetting. Before diving into the carbs, though, make sure you understand whether the rest of the bike's engine design features will support a carburetor change successfully.

Bill Silver