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Su Carb heated manifold adaptors
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jessejazza



Joined: 18 Mar 2009
Posts: 75

PostPosted: Fri Dec 20, 2013 10:06 pm    Post subject: Su Carb heated manifold adaptors Reply with quote

I read somewhere along time ago that the SU manifold adaptors were heated as this helps the atomisation of the fuel. So what happens if one doesn't connect the water hose to them?

I've just been looking at a few older motors and Volvo 121 didn't have them but the later 240 did. Then I noticed that Stromberg CD carbs didn't seem to have them.

So how much of a difference does it make? I was thinking of leaving the hose off as I have got a rusted thro' core plug and was thinking as I am rearranging the cooling system of just leaving it out.
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Penman



Joined: 23 Nov 2007
Posts: 4748
Location: Swindon, Wilts.

PostPosted: Fri Dec 20, 2013 11:30 pm    Post subject: Reply with quote

Hi
Not sure about them BUT I know, from bitter experience, that if the air intake spout on a 340 isn't directed down to the exhaust manifold in the winter (or the flexi pipe goes missing) then the carb fitted to them will ice up in freezing and damp conditions.

Daft thing is I should have recognised the symptoms as I used to fly piston engines and knew about carb heat on aircraft, it just didn't occur to me that cars could suffer engine icing as well. Rolling Eyes
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jessejazza



Joined: 18 Mar 2009
Posts: 75

PostPosted: Sat Dec 21, 2013 12:42 am    Post subject: Reply with quote

Penman wrote:
Hi
... the carb fitted to them will ice up in freezing and damp conditions.
... that cars could suffer engine icing as well. Rolling Eyes

Some engines more than others and also seems to vary from car to car. I had a scimitar that never suffered carb icing (38DGAS Weber carb on those). Like you I have experienced carb icing when the air intake is not directed down to the exhaust manifold.

On the scimitar I had the Ford airbox, and I also tried a K&N (which were prone to cause carb icing) - but I didn't experience it with my car.
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47Jag



Joined: 26 Jun 2008
Posts: 1480
Location: Bothwell, Scotland

PostPosted: Sat Dec 21, 2013 1:13 am    Post subject: Reply with quote

While in Canada I had an Austin 1800 with the engine breathed on to MGB Stage 3 and I had one of the HS6s carbs ice up while the other kept the engine going. When I say iced up I don't mean a wee bit of frost on the surface it was about 3/16" thick all over the carb. I was travelling between Toronto and London (160 miles) on a motorway type road so the speed was constant and these are the conditions that ice will build up. The only way that I found out was I noticed the fuel gauge was dropping faster that usual for this trip so I pulled into a service area to refill the tank and have a look-see. As an aside BMC fitted a band type heater around the piston chambers which I assume were on all the time the ignition was switched.

Art
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ka



Joined: 03 Dec 2007
Posts: 600
Location: Orkney.

PostPosted: Sat Dec 21, 2013 9:26 am    Post subject: Reply with quote

I think it is down to where the air going into the carb comes from, and the length of the manifold. I have run an SU further away from the engine to allow better swirling (different thread) and found this iced in winter, I ducted warm air from the rad around the carb to solve it. I now have the carb above the exhaust manifold (side valve engine) with no issues.
So as to heated inlet manifolds, depends on the ambient temperature, and where the air is ducted from. In a British summer the ambient temperature can vary, but at least by heated manifold, or warm ducted air you will be safe in most conditions, any power loss from the warmer/less dense air would probably not be noticed in our age of vehicles, (this is why turbo-charged vehicles use inter-coolers).
I used to have a Mk1 Escort, where I seem to remember it had a summer and winter setting, turning the air inlet spout from the air cleaner to be in clear air, or above the exhaust manifold.
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