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MG MGB Technical - Crankcase and Carb?

Hi all-----------
Is there any change if the crankcase breather hose is hooked up to the carb or if it is not and instead to open air? Also, will the carb draw more gas from a start with a lighter damper oil or a heavier oil?
Thanks for any info!
Dale & Barb Mast

Lighter oil will provide faster response from the carbs. 3-in-1 is frequently recommended here.

Hooking your breather up to the carbs may suck oil into the intake. Probably not a good idea unless you build a better oil separator. If you check the archives, you'll probably find some good info on that.
Jeff Schlemmer

Hi Jeff-----------
Thanks for your reply! The twins are out of the car and as soon as I get to it, the complete conversion will have a for sale sign on it. That front pipe is a Bell S/S and the exhaust manifold has been sent away and aluminized for those twins.
I went back to my old faithful HIF-44 single and it runs very well! I have a little stalling taking off and figured the oil (20w50)is a little to heavy. A lighter oil is probably what I need then?
Dale & Barb Mast

Dale. MGs have used the "closed circuit" engine breather since early MGB production. The system is set up to work with it. I, on the advice of Bob Ford at Brit-Tek, tried to use the "road draft tube", but the car seemed to use more oil. Hooked the tube up to the air cleaner (Weber conversion) and all has been well since. Yes, some minor oil fumes do settle out and give a trace of oil residue. But, this has never been a problem on either of my two cars. Les
Les Bengtson

Lighter oil will allow the pistons to rise faster when opening the throttle for accellerating, it has little effect when starting the engine, unless you start the engine with quite a large throttle opening which shouldn't be required either hot or cold. If they rise too fast you will be losing out on the required enrichment for accellerating which can cause hesitation. If too thick it will richen for longer than required and so use more fuel.

The crankcase breather connected to the correct carb port gives positive crankcase ventilation, which prevents internal condensation and corrosion, as well as burning of any fumes which stops them getting into the cabin. Just leaving the crankase vent open to the air will give no through flow of ventilation, which will be worse than the early road draft tube system which at least had the other (rocker cover) end connected to the air filter and so may have given some suction under some circumstances. If you did this without sealing the carb ports you would grossly weaken the mixture, upset the mixture balance across the range if you corrected the weakening at idle, and draw unfiltered air into the cylinders.
Paul Hunt

This thread was discussed between 18/05/2005 and 19/05/2005

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