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Engine And Carb Breathing

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#1 FDW

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Posted 04 September 2019 - 09:05 PM

I have a few questions about my 998cc 1990 Mini Mayfair

 

So, at current the overflow pipe on the float chamber for the HS4 carb has a simple vented plate over it rather than the pipe, as a lot of people do. The metal pipe from below the sub frame is still there just disconnected. Is it better to have the overflow pipe connected or not? I'm thinking to keep the plate as if the carb is working just fine it shouldn't cause problems and if not, then the plate will raise the problem quicker, albeit a bit messier. 

 

The second question is about engine breathing, right now it has a canister from the timing chain cover that is connected to the carb and no signs of having a breathing canister at the crankcase as the mounting point is solid. Is it better to just keep this setup or think about upgrading it to a case that can have a breathing canister fitted there as well - baring in mind it will be daily driven one day. And finally could someone explain the setup between the two breathing canisters and the carb using a y-piece. 

 

Still learning my way around my mini so thanks for any corrections or help!

 

Fin



#2 nicklouse

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Posted 04 September 2019 - 09:18 PM

Sounds like you have had a carb or an engine swap at some time. The carb breather plates were not really a add on.

You don’t need more breathers and that is how the 998 came.

#3 unburntfuelinthemorning

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Posted 04 September 2019 - 09:30 PM

If your float chamber overflows the petrol will drop onto the exhaust, if the overflow pipe is connected then the petrol is directed away from the exhaust.  Only fitted from 1980 ish so all earlier cars overflowed onto exhaust.  Doesn't seem to have been a major issue.  I'll have the overflow pipe if you don't want it, I've been looking for one for mine.

 

998 Minis normally have a breather canister attached to one of the tappet chest plates behind the exhaust manifold.  The timing cover one will do the same job.  So does yours have one or two breathers?  Not sure what you're asking but air is drawn in and filtered via the oil filler cap (which is a service item) drawn through the crankcase and out through the breather canister and then into the carburettor where the crankcase fumes then mix with the air/fuel mixture and are combusted in the cylinders.



#4 Ethel

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Posted 05 September 2019 - 07:45 AM

The function of the carb float vent is principally to equalise the pressure inside the float chamber. Your float lid, at least, is from an earlier car. I don't see it as a major issue. As you say, if it did overflow you're likely to smell it. If petrol doesn't ignite in right proportion inside a hot engine until the plug sparks, an exhaust pipe isn't going to do it either.

#5 FDW

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Posted 05 September 2019 - 08:56 AM

If your float chamber overflows the petrol will drop onto the exhaust, if the overflow pipe is connected then the petrol is directed away from the exhaust.  Only fitted from 1980 ish so all earlier cars overflowed onto exhaust.  Doesn't seem to have been a major issue.  I'll have the overflow pipe if you don't want it, I've been looking for one for mine.

 

998 Minis normally have a breather canister attached to one of the tappet chest plates behind the exhaust manifold.  The timing cover one will do the same job.  So does yours have one or two breathers?  Not sure what you're asking but air is drawn in and filtered via the oil filler cap (which is a service item) drawn through the crankcase and out through the breather canister and then into the carburettor where the crankcase fumes then mix with the air/fuel mixture and are combusted in the cylinders.

Sorry yep my mistake it is just the one canister on the tappet chest plates as standard. And for the overflow pipe, I have no idea when I'll be able to get it out at the moment but when I do if you don't already have one I'd be happy for you to have it.







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