XS650 Short Style Breather Modifications

This conversion doubles the flow of the stock late model breather assembly.

Restrictive (short) late style breather (left) and the low restriction early model long dual outlet breather (right), it has two 3/8 inch outlet holes and a double the stock size oil separator metal baffle hole inside. This big assembly causes carb mounting interference problems and Yamaha discontinued it, but the smaller replacement design it not big enough for a stock motor, much less a bored, performance tuned or stroked motor.

The small holes in the stock breather housing and stock baffle plate shown above can cause the cam chain tensioner rectangular cover gasket, the cylinder base gasket, the clutch push rod seal, and the countershaft output shaft seal to blow and or seep or leak oil due to excessive crankcase pressure.

The stock late breather outside cover viewed from the inside, the hole is fairly large until the small restriction at the end.

I drill the breather restriction to 21/64 th or .328" in a drill press vise from the inside.

The 21/64" new hole removes the small restriction at the outlet.

The 21/64" new hole from the outside, compare this to the top two images on this page.

Only the small bottom hole in the metal baffle gets enlarged to 21/64", a file or small grinding stone is best for this because the thin oil separator baffle is very thin tin, and may be ruined or hurt you when trying to drill it, so grind or file it slowly. Then I bend the 90 degree stock metal baffle 45 degrees, this lets air past it, and it will not be bent down so far that it hits the cast radius for the 2 bottom bolt holes when it is reinstalled. See the stock meatl baffle view above.

Here the modified metal baffle is installed back in the breather housing with the enlarged hole. You snap or push it in or out to install or remove it. You can see the 90 degree baffle on its new 45 degree angle inside the enlarged hole.

This is where the breather assembly bolts on to the head, top hole (arrow) is the oil return drain hole for oil that goes into the breather assembly, use caution with gasket sealer on the breather mounting gasket because it can block the small oil return hole that allows oil to return back to the crankcases. Bottom arrow is on the passage that the oil returns in. Note the red/orange silicone inside the oil hole shown at the top arrow, see the image below:

This is the excess silicone that was blocking the oil return hole I removed from the head above, previous owner or mechanic used to much sealer on it and it made this perfect moulded plug to block the oil return hole inside. Seals were leaking and the tensioner gasket was blown and draining oil on top of the crankcase that runs along and follows the base gasket on the left side because of the side stand bike position, it appears to be a base gasket leak, but is a tensioner gasket leak usually.

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