If you don't plumb it to the inlet it won't actively draw the blow by from the crank case in turn contaminating the oil sooner as long as you change the oil regularly it won't matter you can just put a small pod filter on it...

ok thanks,so ill need to make sure the thred in the new manifold is the same and replumb it!

It can vent to atmosphere, but then it doesn't work as well and you might smell the fumes sometimes

im about to fit a single dcoe weber to my a15,does the crankcase breather still have to go to the inlet manifold? or can it just vent to the atmosphere? cheers Barry!

the pressure is mostly due to blow-by and crank rotation, so it's mostly in the bottom half. The early A-series had the top half capped off with the above-the-head space vented via the head's oil drain holes, then to the bottom breather tube

Bob,it,s there to remove any crank case pressure,if it cant get away it'll go out past the rings..... or blow out the front or rear seals

Quick question.
Do we need the bottom breather on the A series motor or can it be capped off and only use the rocker cover breather ??
Thanks