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INSTALLING #14155700 ENGINE BREATHER
Your original air filter also served as an engine breather devise. Since you are now removing the original air box, this kit will replace the now-missing breather function.
What does an engine breather do? Any engine produces pressure in its crankcase during operation. This is due partly to heat expansion but mostly to the natural leakage past the rings. The problem is that this excess air volume also contains a lot of oil which must be separated out and returned to the sump if we expect the engine to run farther than five miles and to not leave a trail like a snail.
The ugly little black box in this kit with three various-size tubes on its bottom and two small ones near the top was originally fitted to the V7 Sport, 850-T, and LeMans 850. The large bottom tube receives the excess air and oil from the engine. It leads to a one-way valve that limits the amount of air drawn directly back into the engine as it cycles. Along the welded joint of the black box is a screen that separates the oil from the air. The running engine draws the oil from the box through the smallest steel tube on the bottom. The medium-sized bottom tube is the vent outlet. The two small tubes at the top of the box are for the valve cover vents that allow water vapor a place to escape.
You may find it easiest to remove the left-hand carburetor to simplify removal of the old air box and installation of the new breather. Save the hose clamps connecting the air box to the engine for reuse in the same location. Your bike may have come with a ball check-valve inserted in the larger of the two pipes sticking up out of the engine. It may now be inside the larger rubber elbow with the air box. No matter - it tends to stick and so we suggest an updated part. Caution! Install the check valve into the large breather pipe out of the engine; do not install it into the black breather box!
With the check-valve in place install the new breather via the two short pieces of hose and secure it with the stock hose clamps plus those prescribed. The valve cover vent lines are either too short or too old and leaky for reuse. Give the hoses a little tug to remove them from the valve cover banjo fittings. Replace the hose with an appropriate length of the new hose from the kit and secure both ends with hose clamps. We use about 16” for the left hose and 17” for the right.
Fit and secure the vent hose to the medium-size fitting on the bottom of the breather unit and route the hose between the transmission and the starter in such a way that it isn't pinched shut. Moto Guzzi does make a bracket to hold the bottom end of the vent tube but it is sized in such a way that a hose that fits it doesn't fit the breather, so instead we suggest a simple little nylon tie. Tie the tube to the frame in such a way that it is clear of the exhaust and the center stand.
When refitting the carburetor it really is OK to reuse the inlet gasket as long as it didn't get too torn up. Do put a dab of liquid gasket on it though, because intake leaks are deadly to engine performance.
QTY / PART # / PARTS NEEDED1 / 14155700 / breather box
4" / 5/16” hose
4" / 3/4” hose
1 / 28150560 / ball check-valve
3ft / 5/16” hose
2½ ft / 5/8” hose
5 / ABZ 8X14 / hose clamp
2 / ABZ 16X25 / hose clamp
1 / 8” black zip tie
CHS 1557