My Honda CBF250 has recently developed a small but annoying fault. At its usual cruising speed of about 60 mph it occasionally stutters. It feels like it's about to run out of fuel. Otherwise the bike is running fine. I checked the spark plug, air & fuel filters, cleaned the carb and even replaced the coil with no success.
I then found reference to running problems associated with a faulty air injection valve. This is located behind the cylinder head and has a pipe running to the cam cover and the air filter. A smaller pipe runs to the inlet. I assumed that this was for emissions reduction. I don't know how it works. A breather from the engine to the air box is ok and I guessed that the pipe to the inlet was a vacuum switch but why? The unit is called the "air injection control valve" in the parts book which implies that it supplies air to the inlet, but that would seem to affect the mixture. Anyway I disconnected the inlet tube and plugged it. After a run today it seems that problem has gone.
The valve does not appear in the Brazilian repair manual I have so it seems it's not vital.
|Air injection valve|
|Pipe to inlet blocked|