BSA Breather Information
BSA A7/A10 Breather Modifications
BSA A10 breather hole location ½” to the right of mid-point of ignition system hole
The stock timed breather no longer functions correctly with an offset crankshaft engine. A new line needs to be installed on a spigot next to the ignition unit. The breather hose is installed before the ignition unit is mounted as the hose clip holding the line in place may not be accessible after the unit is installed. The new line is a rubber oil line connected to the stock breather line. Do not use a clear plastic line. The breather line, with its connection to the oil tank, should then be connected to a Yamaha XS650 reed valve as this helps create a partial vacuum in the engine which improves engine performance.
A modified stainless steel bolt with a hole drilled through it is supplied with all BSA A7/A10 crankshafts. Instructions on how to install the breather spigot, and a schematic of the breathing system, are supplied with this crankshaft too.