CBX550 air filter drain plug.

Apparently the crankcase breather is plumbed into the filter box and has a
sort of plastic sump bottle to catch any emulsion etc blown out of the
breather.

I've been told that this needs to be drained occasionally otherwise the
filter cartridge gets oiled and ruined.

As I intend to replace the filter fairly soon, I looked it up in the Haynes
manual and went outside to remove the drain plug as instructed -
unfortunately, on finding the pipe in question, I discovered that said plug
is missing.

Is it important? - What are the pro's & cons of leaving it as is/ finding
something to replace the plug?

TIA.

 

Find "something" to plug the hole with, even if it's only duck/gaffer tape.
Otherwise the engine will be sucking air thru the hole, by-passing the
filter and can ingest all sorts of muck.

If the engine's done a high mileage, it would be a good idea to replace the
existing pipe with a length of (heater) hose running from the engine to the
back of the bike; e.g. a small hole drilled at the back of the mudguard for
a tie-wrap keeps it neat behind the numberplate. Don't forget to then
block-off the stub where the pipe would normally connect to the airbox.

This mod lets the engine run on clean air instead of it's own farts.

 

Thanks.

 

If its bleeding air after the filter it might account for reluctant starting
in the cold, the bike has a plunger jet choke instead of a flap choke -
whatever difference that makes.

Looking at the spark plug colour I'd say it was running slightly lean, but
as I stick to speed limits and rarely use motorways, fixing it hasn't been a
priority.

 

A four has 2 up & 2 down - I'd expect the pressure to cancel out, as its 27
years old I'd expect some pressure due to blow-by.

But the breather is

Free upper cylinder lube?

I don't think it's anything to do with

The breather on a CB200 is just a pipe that hangs down behind the lump, with
2 pistons going up and down together the crank case alternately sucks &
blows, I'd always assumed that condensed oil mist on the inside of the pipe
made it sticky and trapped any grit that got sucked in.

Its a pretty old bike so I'm not looking to increase performance in case I
finish it off.

If the air bleed is saving me petrol I might leave it as is, as for the risk
of sucking in crap and causing damage I've only just found out the plug was
missing, so it probably wasn't there when I bought it a few years ago and
who knows how long before that - pretty much a case of shutting the gate
after the horse has bolted.

If it improves cold starting I'm likely to fit a plug, I've no plans to
modify the system.

Thanks all for the advice.

 

Er, as I understand it. Crankcase pressure is as the result of
'blow by'. Which you get quite a bit of until the rings have
seated properly.

 

Hence high performance race engines run the CC under vacuum.

 

On a nicely warmed up engine with above mod, it is quite amusing to see
the puffs of steam exiting the end of the bike.