22 replies to this topic

[Vipernoir]

In over 50 years of playing about with Minis I have never run water heated manifolds and have never had any carb icing issues. The early cars, when modified but retaining small carbs had this issue, but larger carbs don't tend to ice. An HS4 on a 998 or HS6/HIF44 is unlikely to ice up on a 1275. Twin SU's are not known to ice up at all - well maybe in minus 40 degree environments they might!

 

I've had twin HS2s freeze up on a 998 and stick the throttle open more than once.
HIF38 froze up on a 998 regularly.
HS4 froze so badly on a 1098 the dashpot was covered in ice - I have photos somewhere.
Twin HS4s can freeze on a 1275, even when it is mild.  On the way back from the IMM in May we had them freeze on the Autoroute requiring a stop to thaw out due to high humidity.

 

Constant throttle opening on a long run will cause icing far faster than on-off activity - such as rallying.

[minimadles]

The only carb that I saw any signs of icing where the ford vv carb they had a vac unit and tube that took warm air from the exhaust manifold into the intake pipe for the air filter

[Vipernoir]

Standard airbox.
Standard airfilter.
Definitely iced...

 

Twin carbs on any size engine can do the same - I've seen it.

[the_samkingdon15]

it's on a metro A+ 1275 so I guess it would have co was standard??

[Tamworthbay]

Standard airbox.
Standard airfilter.
Definitely iced...
 

Twin carbs on any size engine can do the same - I've seen it.

But as there is a half inch thick spacer acting as a heat shield between carb and manifold then gently warming the manifold won't help this problem anyway.

[HUBBA.HUBBA]

you could put a heater element in the air filter, like what us sc chaps do.

[jaydee]

 

 

Constant throttle opening on a long run will cause icing far faster than on-off activity - such as rallying.

 

 

This can explain why with twins + trumpets on motorway journeys when i come to a stop idle is sky high then restores after a minute of idling

I thought it was something timing related

Never had this with the HIF44, but got a frozen HS4 once

[GraemeC]

The heated manifold is not to help come off choke quicker - they were plumbed after the thermostat so would offer little extra warmth to the charge whilst the engine was still cold.

The main reason was that they gave a constant charge temp which made emission control and engine tuning more predictable. Maybe at a slight loss of power but economy improved as the engine could be tuned more accurately as it would run in more regulated condition - ie not have to be able to work with such a wide range of inlet charge temps.