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MG Midget and Sprite Technical - inlet manifold

12CC engine...standard spec. The crankcase breather vents into the inlet manifold...but is the manifold "hollow" across all four inlet valves? Is that even a question?...Does the vented vapour get fed in to all four cylinders? many thanks, chaps... Dave
David Cox

Dave,

I believe that since that tube is hollow and joins the two inlet ports, when an inlet valve is open, it pulls fuel from the carb and whatever comes into that tube from the crankcase breather. So, yes, all four cylinders get fed the vented vapour.
Martin

Don't forget there should be a valve that limits the vacuum otherwise it would upset the fuel/air ratio. Having said that the extracted fumes will be burnt by all 4 cylinders.
The tube is hollow inside and is an attempt to even air flow through the 2 carbs which does improve fuel consumption.
Rob
MG Moneypit

thanks, both. Dave
David Cox

Rob
I didn't think the later 1275 had a vacuum valve, well mine (12V in a Frogeye) hasn't - the breather hose goes directly from the metal canister (with gauze filter, attached to the timing chain cover) to the carbs/ manifold.
Bill Bretherton

Bill, there is a very significant difference between the breather hose going to the carb, from the version with the hose going to the manifold. The suction is completely different when to the carb where it connects to the upstream side of the butterfly.

It has all been discussed here before, in very great detail!
GuyW

Guy

Oops! Thanks for the clarification. I didn't realise earlier 1275 cars' breathers connected to the manifold like earlier engines. I've now checked in Horler and the change came with the 12CE engine.
Bill Bretherton

Bill,
David has early 1275 the 12cc. See below for set up.

ETA: oh, you posted whilst I was looking for the image in my files, oh well, a picture ... as they say.



Nigel Atkins

Thanks Nigel. For some reason I assumed all 1275 engines breathed via the carbs. That'll teach me to check first before posting!
Bill Bretherton

Interesting. I have a 12cc engine and the breather goes straight into the carbs. Originally they were HS2 but are now HS4. Can't really see the difference unless its for originality.
Bob Beaumont

Bill,
I'd forgot previously until Colin reminded me which is why I knew I had that drawing.
Nigel Atkins

According to the service parts list AKD 3513 the change point for the crankcase breather system being linked to the carbs on 12CE engines was after engine no. H3400.
My midget 12CE engine no. H3-- has the diaphragm valve on the inlet manifold.
J Bond

This thread was discussed between 11/05/2022 and 24/05/2022

MG Midget and Sprite Technical index

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