Hi,
I have just bought a 1980 V50 Monza as a part-finished restoration, and the air filtration and crankcase breather apparatus are clearly non-standard.
Is there a diagram anywhere which shows what the system should look like?
If I decide to get individual cone filters for each carb, what hardware do I then need to install to complete a crankcase breather system that works?
Hello and welcome to the forum. I know the air filter box is a pig to get in and out of the frame and so many have changed to individual filters.
There has been discussion about this recently and I am sure someone will come along shortly with the answer!
Best wishes Chris
It is very tempting to fit individual filters the original filter gives a lot of filter area and the air box recycles blow by gases but as a result it is enormous and a real skill changing them without bloodshed lol
Back when i used to work on these we fitted Uniflo foam filters as we reasoned that you can see through a K&N so it is a strainer rather than a filter and not a good idea on an engine you want to keep! However we found that many bikes with on-carb foam filters of any make started and ran really badly after rain. It appeared that as that they sit just under the front corners of the seat rain runs off the seat onto the filter effectively clogging it up until the engine sucks it dry, giving poor starting and running. So if you do fit them i advise making up a cover to deflect the water that will drain forwards out of the seat!
Hello again,
If I go for the individual filters, what do I need to do with the two rocker cover breathers and the crankcase breather?
The bike had a cannister to which these three pipes were connected, but this was clearly not a Guzzi item, and I don’t know what it was for. It was also full of rust, so I’m inclined to bin it!
Well, as you know, the original method runs the blow-by oil mist from inside the engine back through the intakes to burn it.
That is really hard to do without the filter box so you have 2 choices.
(1) run it to a catch tank or bottle which you empty when it is full
(2) run the three pipes to ground between the swing arm and gearbox
That’s great. Thank you.
A friend of mine ran the breathers into a Guinness can that matched his black and gold colour scheme. 
I run a V50 with pod filters . I made this up using a Y branch l got from an aquatic shop. You can get internal Y branches, but l thought the bigger bore would be better . Cheers.
That looks good. I’ve ordered some tube and a Y-piece much as you describe.
One question though: The breather that comes from the back of the engine sump: I took the tube off, and a significant quantity of oil then drained out of the spout left behind on the engine. Is this normal? Is the spout below the surface of the engine oil in the sump, and if so, how does this outlet act as a breather for the crankcase? I’m well confused!
The return to the sump ? Think it’s below the normal oil level , so there will always be some oil in the tube .
Yes the connection low down back of the sump is not a breather it is for the return of oil that has separated out of the blow by in the air box.
You definitely don’t run that to ground lol
Many thanks for all your help.
Just to be clear then: There are probably three options here, assuming that I am using individual filters:
Which would you recommend?
This thread could become a science project all of its own, which means I don’t really understand what the breather system is for, and what the anatomy is supposed to look like. I assume that the crankcase (i.e. below the pistons) must be able to vent excess pressure (blow-by), so how does it achieve this on the Guzzi engine?
Thanks again.
As far as I am aware Guzzi let their engines breathe from the top of the cylinders to allow for air movement caused by piston movement and blowby. In the small block engines this is is from the rocker box.
The breathing goes to some kind of reservoir to allow gas and liquid to separate (In V50 that is the air box). Liquid then drains back to the sump.
A sweet project would be to mount a transparent container in the space between the filters with 4 pipe fittings. Run pipes from the rocket box to the middle, the drain to the sump from the base and a vent tube from the top looped down to ground. Bingo your own ‘seperator’ and you can see if the engine starts breathing more oil.
