Carb Mounting

[alfadave]

I understand Lotus used the flexible carb mountings with O rings to prevent frothing.

Seems that on the 105 series Alfas of the period, paper gaskets were used.

I'm just about to take my Weber DCOE carbs off.

Has anyone else used paper gaskets with success?

[alan.barker]

"O" rings are ok why reinvent the wheel.
They have a good track record lol.
Maybe Alfas would be better with "O" Rings
Alan

[elans3]

Don't use paper gaskets. Remember the Alfa originally had rubber carb mounts to control the frothing, and they only needed the paper gaskets to seal the carbs to the mounts. They then had to mount a stay between the block and carbs to stop the carbs wobbling about so much !
I have solid carb mounts on my Alfa, (with Misab O ring plates between the carbs and solid mount inlets), but still use either rubber bobbins (Cosworth type), or thackeray washers to give the flexibility needed to control the frothing.

[Craven]

I’m sure frothing can be woven into the rubber mount theory but from comments made on a BRM built twincam after use in the 1965 Alpine Rally to determine engine condition following comments were noted,
15, Carburettors & Gaskets
Double ‘O’ ring gaskets of the Latest Lotus Specification, ie Alloy plate and ‘O’ ring each side. No failures occurred during Rally with this type, all 1965 Alpine Rally engines were fitted with these.
No failure on this engine of the Double spring washers on carburettors retaining studs has occurred.
During strip down the inner ‘O’ ring of No3 cylinder had started to break-up, the remainder were OK.
These comments makes me think there was more of strength and shock absorbing issue being design tested here.
FWIW.

[512BB]

Of course the other benefit of using the correct misab plates, is to insulate the carburettors from heat. If you were to just use paper gaskets and no misab plates, at least I think that is what is being suggested, the carburettors would heat up to a similar temperature as the head, and that would not be ideal.

I have pictured the other mickey mouse set up that I would never use. Removed from an engine that was impossible to get to run correctly. Fit the correct misabs, you know it makes sense.

Leslie

[john.p.clegg]

.. and source / fit some nitrile / neoprene O rings for them.....buy them in bulk and sell off the rest here..

viewforum.php?f=33

John

[alan.barker]

Spot on Leslie 100%
Alan

[alfadave]

I've already got the correct misabs / O rings.

I'll leave the carbs on, and leave well alone.

[snowyelan]

Neoprene isn't compatible with gasoline, and Nitrile is marginal when exposed to ethanol based off of Parkers compatibility charts.
There's a few options left now due to the witches brew from the pumps.

[2cams70]

My preference is not to use Misabs but to use the alloy block spacers with O ring grooves either side same as Lotus used originally. QED supply repros. That way you can just use standard O rings of whatever material you choose.

[StressCraxx]

Neoprene isn't compatible with gasoline, and Nitrile is marginal when exposed to ethanol based off of Parkers compatibility charts.
There's a few options left now due to the witches brew from the pumps.

Viton (flourocarbon) is widely available at most bearing/hydraulics supply houses and works perfectly well with road fuels and race gas.

[john.p.clegg]

My preference is not to use Misabs but to use the alloy block spacers with O ring grooves either side same as Lotus used originally. QED supply repros. That way you can just use standard O rings of whatever material you choose.

I was sure the original plates were called " Misab " after the manufacturer ?

John

[alan.barker]

when i fit the "O" rings i put some silicon grease on them. That way they settle into place nicely.
Alan

[2cams70]

I was sure the original plates were called " Misab " after the manufacturer ?

Misab is the original manufacturer of those thin Aluminium plates where there is an O-ring moulded around the plates. The "O" ring (one only) is integral with the plate and non-replaceable. The pictures 512BB posted earlier are Misab style but probably not original Misab (original Misabs have "Misab" stamped into the plate)

The Lotus originals were thick Aluminium spacers with grooves for two replaceable O-rings - one on each side of the spacer.