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Rubber mounted SU carbs
#1
Although not for an Austin Seven I hope someone may have the answer.
I have a pair of 1 3/4 SU carbs originally fitted to a TR7,They are still pretty much as vintage carbs but mounted on rubber mounts.On Most vehicles earlier the carburettor was bolted up solid with a heat insulator spacer between.
Can I ditch the rubber mounts,or would I be best to keep them ?
I am fitting them to a Model A ford engine and have an aluminium manifold to adapt them to.
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#2
What model of SU?
Will they be sitting at the same angle as originally fitted?



Paul N-M
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#3
I had these fitted to a TR4 without a rubber mount. I think there was an insulator between the carb and manifold. They worked really well.
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#4
Actually I think they are HD 6 or 8's. Anyway I would not bother with them and just use std. SU insulating spacers. I run 2 x HD8's on long manifolds on my Bentley special and have never had a problem with vibration. Also I suspect they are prone to failure from the very vibration they are trying to dampen as the weight of the carbs will lead to cracking over time as I'm sure they will not have any additional support.
I think Rover also used them on the 2200 TC with out insulating again with no probs as did RR on the 4.9 S1 type engine.
Maybe the TR engine had a particular issue with vibration?

Paul N-M
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#5
The TR7 engine was basically a Dolomite engine; on the Dolomite the Stromberg carbs used an asbestos (?) heat-insulating gasket, but when the Sprint went rallying and racing with SUs they suffered from fuel frothing in the float chambers so presumably this was the reason for fitting the rubber gaskets on the TRs. If I recall correctly the frothing occurred at something over 7000 revs, so was unlikely to occur under normal road conditions, but BL played safe.
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#6
Thanks for the replies I think I'll make the flanges to bolt straight to the carbs with an insulator .In the TR the engine was canted over and made for a longish inlet manifold,perhaps this too was part of the problem.
I had emailed Burlen for advice but not received a reply.
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#7
When removing the carbs from my Armstrong Siddeley Star Sapphire, I found thackeray (double-coil) spring washers under the mounting nuts. 
After asking around I found that they are correct and need to be used with a resilient joint packer between carb and manifold.  They say it reduces the transmission of vibration from the engine to the carb.  Apparently you do the nuts up tight and then back off a bit (don't know how much but half a turn sounds about right).  I thought it was all wishful thinking but several different cars including TRs used this method so I guess it works.

Ivan
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#8
DCOE Weber’s use a similar system to insulate from engine vibration
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#9
1960's Lotus Elans have the same system
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