With a standard 711 cross flow breather what’s to stop it sucking in air thro the vented filler cap down thro the engine & into the inlet manifold weakening the mixture.

Engines normaly blow not suck,so it pushes air out of the cap.

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Originally posted by johnwilders
With a standard 711 cross flow breather what’s to stop it sucking in air thro the vented filler cap down thro the engine & into the inlet manifold weakening the mixture.

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With my xflow, im sure there is to much pressure in there, as its seems to spew oil from every possible place !

If it was sucking air in, my oil level would get higher !

As Steve M says. Crossflows are designed to blow oil out, not suck air in.

If the breather was connected to the manifold it could draw air from the crankcase (depending on the strength of the spring in the oil collector one-way valve).

However I think that the crankcase breather vents into the air filter in a standard factory car installation. I.e. it's connected upstream of the carb so it doesnt weaken the mixture.

Thanks Dave, you seem to be on the same wavelength, I was thinking maybe it has got the wrong cap. The crankcase breather from the oil trap appears to have been vented to a T on the inlet manifold, the other side would have gone to the servo. I think the valve in the oil trap is just a flashback arrestor & doesn’t restrict the flow from the crankcase so the depression/vacuum in the inlet manifold would draw air thro the vented cap rather than just excess crankcase pressure.

back when i had a crossflow, it would dump a pint of oil out in 5 laps so just as well mine wasnt plumbed to the inlet, as it would probably die with that much oil going in!