Carb throttle discs.

[john 4d]

My carbaretors have throttle disks with vent valves, see photo.
My search explaining them on a Stag has drawn a blank. I found the picture on a Moss web site attributed to MGs and dates between 1975-1980.
Does anyone else have them?
Are they suited for a Stag?
What function do they provide?
Regards
John

[Lingen]

John.
Thy were latterly fitted to Stags to reduce exhaust emissions when the engine is on the overrun and the disc valves are closed. They can be troublesome when tuning the carburettors, and the usual advice is to solder them shut and forget about them.
Mike.

[Goldstar]

They are there primarily to screw up your mixture settings and are the work of the devil. As Mike says, either solder them shut or replace them with plain ones John.

[john 4d]

Well, thanks, gents. I was hoping for more comments, but it looks like we already have a consensus.
John.

[Philip Wardle]

The Haynes "Zenith Stromberg CD Carburettors” manual says the poppet valves found in some throttle plates are a means of limiting "the very high manifold depression which occurs when the engine is in the over-run condition", this condition being "not conducive to efficient 'clean' combustion". An alternative way of doing this is the by-pass valve. One or other of these devices (but not both) were fitted to Stags exported to markets where more challenging emissions legislation and regulation were being introduced. As far as I know, neither device was fitted to UK Stags but I guess they were introduced to other vehicles sold in the UK that used Strombergs.

The need to respond to emissions regulation was one motivation for development of petrol injection but early injection systems struggled to achieve any improvement over carburettors. The poppet valves and by-pass valves were really sticking plasters to extend the useful life of the Strombergs while electronic controls for fuel injection were being developed. But although limiting the manifold depression helps with the emissions challenge, it also compromises other aspects of engine performance and the driving experience. This is why the consensus is to disable these devices.

[richardthestag]

They are particularly useless when trying to tune the carbs as their operation is unpredictable.

Certainly telling that you can no longer buy them new!

We were soldering these things closed back in the 1980s

If you really insist I have a box of used items which due to their rarity and curiosity value must be worth a load of money

[john 4d]

Ok.
Pumbing solder with torch or electrical solder with iron?
I guessing electrical, conducting least heat, not risking distortion to the disk?
John

[john 4d]

Someone's listening!
Just opened youtube, only to find on the home screen, Richard Hudson of Church House Classics soldering a throtle disc vent poppet valve!
How weird is that.

[dasadrew]

Someone's listening!
Just opened youtube, only to find on the home screen, Richard Hudson of Church House Classics soldering a throtle disc vent poppet valve!
How weird is that.

Really weird - two people called Richard doing this; I mean, what's the probability of that??

[richardthestag]

Someone's listening!
Just opened youtube, only to find on the home screen, Richard Hudson of Church House Classics soldering a throtle disc vent poppet valve!
How weird is that.

there are a whole lots of Richards out there, in this case we are one and the same, nice to see yootoob not shadow banning me all the time

Plumbing solder, clean the disc, flux the disc and then solder it. If you can solder a pipe joint without warping it then you should be qualified to do this. Else buy a pair of discs from Burlen.

Be aware that the seals on each end of the shaft are likely ancient and will need replacing also.

[john 4d]

Small world. Great vids. Thanks all, and Richard!