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Series 3 petrol breathers


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Hey lads,

This is probably a silly question, and is probably a very basic question. ( for some at least)

On the oil filler pipe and on the rocker breather there is a tube connection, in the past I have always connected these to a vacuum connection, but it then occurred to me that thi cannot be correct, in that wouldn't the fuel mixture be weakened.....? Any clues Fellahs ...?

By the way we are talking about an early series 3, 4 cyl. Petrol engine.



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The breather should connect to the vacuum-side of the inlet manifold, through a vacuum-control-valve:


This valve closes down when the engine is at idle so it stops the air-leak weakening the mixture. At larger throttle openings the valve opens - but the additional air-flow then occurring through the valve is small compared to the volume of air/fuel going through the carb so the 'diluting' of the mixture is marginal.

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My 1972 2.25 petrol has the breather pipe from the oil filler connected to the vacuum control valve, the pipe from the valve then connects to the sandwich plate between the carb and the inlet manifold.

The rocker cover breather pipe connects to the air pipe that goes between the oil bath air filter and the top of the carb.

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