MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - What to do with breather when Weber's installed?

I've put a Weber on my engine and was wondering what others do with the engine breather. I assume if it's not connected up then the rear scroll will leak. I did have a bit of a look in the "engine breather" thread but at 350 posts it's a bit overwhelming for me. I plan on blocking the rocker breather up.


Greg H

Find one of the early 'diaphragm-valve type' breathers and pipe this in the line to the inlet manifold.

A
Anthony Cutler

I have one of those diaphram valves from my twin SU's but that connected in via a balance pipe which I now don't have. So how would I connect it in?
Greg H

straight into the inlet manifold (either arm).

A
Anthony Cutler

Mine vent (I have one on the fuel pump and the usual one on the timing case) to a catch tank.

It's not perfect, because there seem to be quite a lot of fumes that come out, so I've been thining about putting them into the rocker cover and then venting that to the catch tank.
OrangeSpyderMan

I have a dellorto, very similar to ther weber. The timing case cannister is connected to the inlet masnifold via the psv.
I once failed to reconnect the psv to the manifold following some maintenance. With a slightly worn engine and the outlet from the timing chain cover effectively sealed I was surprised at just how quickly oil spewed out the scroll onto the garage floor
With everything connected as above its just a drip
S G Macfarlane

would that rocker cover be original then and with top vent pipe?
Nigel Atkins

I'd be inclined to run a breather pipe into a catch tank from the timing cover and from the rocker cover take off - then you don't need to worry about octane reduction from oil fumes.

That's a very short K&N filter - there must be very short ram pipes underneath - if you don't have clearence issues you might like to consider a larger filter and longer ram pipes which should give you more torque...
James Bilsland

Had mine plumbed in with a pvc valve and It surrered from pinking due to the octane reduction from the oil fumes.
Now it just vents throught the splash panel to the atmosphere.
Leaks you ask? Sure but then this engine is bust so It will have to survive until the fresh engine is finished.
Onno K

If you have that level of fumes (using diaphragm-type valve), then your engine needs a rebuild. Any venting of the crankcase to atmos will ensure leaks from the rear scroll - you can't obtain a vacuum in the crankcase unless the rocker cap is the correct one, and there are no other vents. This is how the engine is designed to operate.

You could try a catch tank between the timing cover and the valve - e.g. even a steel or copper coil that would allow fumes to cool, condense, and drain back into timing chest.

A
Anthony Cutler

Nigel are you having a little dig? Next you'll be onto me about the green stator in the alternator. :)

I feel I need something to keep the vacuum in the engine. I think when it was on before I just had a hose from the timing cover into the air filter. Would that work ok?

Ideally I'd like to make a balance pipe out of aluminium tube and weld it inbetween the two inlet pips with a T out the top, but a bit of effort to do this. I could try connecting it to one inlet but feel this could upset the tuning of the engine. Onno's comment seems to support this. Thoughts on this?

Greg H

James got the short filter as i didn't know how much clearance I'd have. I may put a wider one on later if I can. Ram tubes you say? They're so short you can't even see them. I thought about it but it's only a road car so I didn't bother.
Greg H

Greg,
if I was having a dig I wouldn't be that subtle, no sorry it was my poor typing in a rush

what I really meant was is the rocker cover with a top pipe the original type of rocker cover when a Webber was fitted

top pipes I've seen go into the black pan looking original type of air filter housing, I've no idea what type of filter housing originally went with the Webber as I can only remember ever seeing them with K&N

now :) is that K&N filter original when the car was new :)
Nigel Atkins

Yes Nigel, along with grey cockpit moulding the Aussie cars were fitted with Webers from new to better accommodate the open road driving. ;) Not sure about the K&N, you could be right there, it may not be OEM.

Most Australians see SU's as quirky English carbies that need to be replaced at the first available opportunity, hence no Su's on mine, although I may put them back on one day for the quintessential English feel.

Greg H

Webbers over SUs I'll leave to the experts, if I was just so unlucky with car stuff instead of buying brand new twin SU I'd have fitted a bigger single SU but if I'd done that something would have been or gone wrong with the installation so I've go the thirsty twins

noticed in Terry Horler's book Aus got wire wheels as standard too which surprised me a bit I'd have thought at the time they wanted the then modern Rostyle (if they were on 69 cars, can't remember without looking it up and can't be bothered to do that at the moment)

anyway be interesting to see the plumbing with seperator, rocker tube and Webber
Nigel Atkins

Hi Greg

I think you will have all sorts of difficulties jetting the carb without any ram pipes - I've never known anyone run a 40/45DCOE without at least short ram pipes. Running without will I suspect give you some strange effects - in particular the airflow through the auxillary venturis will be disrupted quite badly I imagine...

There is usually room under a Spridget bonnet for a 45, a short/medium length manifold and a medium sized filter - on my old road midget I ran a medium K&N filter with a set of ancient group 2 ram pipes underneath (the ones that are 'kicked up' rather than straight out)

James
James B

James they'll be no difficulties without the ram tubes. I've run them before with and without with no problems and last time on this car I had larger chokes so it should be fine. The important thing is it's tuned to suit. i.e. if tuned with ram tubes you can take them of without retuning and expect it to run the same. If I have enough clearance I'll go for a larger filter and ram tubes but I remember last time with this manifold there's very little room and that was with a very thin gauze ram flow filter. Looking at it how it is now I'm not sure it'll clear. I expect to put the bonnet on in the next couple of days so I'll know soon enough.
Greg H

This thread was discussed between 08/03/2012 and 12/03/2012

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.