Reason Triumph used flexible carb mounts originally?

[Sundowner]

Gents,
Before I became aware of the alloy alternative, I replaced the flexible carburettor mounts with the dreaded repro's.
I've read lots about how good this alloy modification is, but I wonder, can someone tell me why Triumph used the flexible mounting system on the original cars, please?
I found that although the originals looked awful externally, they seemed fine internally. I didn't test them to see if they were sucking air but I still have them.
Cheers,
Rob

[TrustNo1]

My guess would be that rubber is a lot cheaper and easier to mould.

[Stevo]

On other cars the use of flexible mounts stopped the engines leaning off under load such as MG's so I would assume they were applied to the sprint to avoid this... but with modern fuel and modern engine build i doubt that this would be an issue now...

[Galileo]

Isolating the carb to stop fuel frothing and heat transfer is the point of them and they are certainly not a Triumph thing as you'll find them in most carb setups from a Solex on a Alfa 105 to a Pierburg on a 1.6 VW Golf.

Are they actually necessary? Many have debated it on this forum alone...

[GTS290N]

I have alloy mounts on my 1850. Never had an issue, unlike the rubber things. Slant has inlet on one side, exhaust on the opposite, unlike some others.

[Galileo]

Exhaust location would only be important for convected/radiated heat reasons, rather than conduction.

[Flyfisherman]

Gents,
can someone tell me why Triumph used the flexible mounting system on the original cars, please?
Cheers, Rob

Rob

Plain and simply - "Vibration" stops the carbs from shaking.

Paul

[trackerjack]

I had solid mounts even before the club made some up because I thought it was the correct way to go.

Old British motor bikes have solid mounts and they vibrate like hell but the carbs cope with it.

I never had problems with the ones I made.

I expect Triumph rubber mounted theirs because the cars came out the factory with lumpy running due to poor setting up.

[Sundowner]

"Thanks for answering, Gents.
What about the transfer of heat from the water heated manifold? Would that have been another reason for their existence?
It gets really HOT here and I wondered about getting stuck with fuel vaporization problems, if I do bite the bullet and invest in a set of the alloy mounts.

[Karlos]

If it was to insulate the carbs from the engine to keep them cooler, wouldn't 1300 and 1500 engines have been a candidate for rubber mounts too? As the OHV engines are not cross-flow there is even more heat to deal with, but then I guess the exhaust proximity made using rubber prohibitive, so they put in the the shield.

On the old Minis, the exhaust and inlet manifold were a one piece casting, with an intense hot spot right above the centre exhaust pipe where the single carb mounted to the inlet. They had no heat shielding in place at all. So the reason for rubber mounts is probablynot a heat issue.

[James467]

Gents,
can someone tell me why Triumph used the flexible mounting system on the original cars, please?
Cheers, Rob

Rob

Plain and simply - "Vibration" stops the carbs from shaking.

Paul

Basically what Paul said.

Early slant engines have Strombergs which have a simple rubber gasket between the inlet manifold and carb body. The carbs are held on with nuts and spring washers which absorb any vibration transmitted from the engine to the carb. The theory is that the carb is isolated it prevents the fuel 'frothing', it's the same setup on DCOE's etc... I spoke to someone from Burlen once and they told me that SU's had more of a tendency to allow the old 4 and 5 star fuels in the '70s to foam up in the float chambers causing fuel starvation issues hence why they had to have a thick mount on them on some cars.

Modern fuels I believe have anti foaming agents added in to them to prevent problems with the modern high pressure fuel systems so the rubber gaskets and rubber mounts aren't really necessary any more.