Carb damper- age?

So after a strip and clean of the carbs, and a long discussion with Tim to work out the adjustable choke/ jets are not original ( so possibly the carbs),

the one damper has lost the valve action ( and the little cross pins in the little piston). After contacting SU U.K. people, they have confirmed very old and don’t have spares so hopefully someone here will know if can fix or replace?
The length from bottom of piston to underneath lid is 3 inches
The lid is vented and script reads ‘Remove and use thin oil monthly’
Has been previously repaired with solder in lid
As unknown when car was last actually running, some of these parts may have been for cosmetic effect!

So you have both a starting carb and adjustable jets? Kind of like the fat guy that wore a belt and suspenders. :grin:
The jet levers are not original, but perhaps you already figured that out.
Carb bodies have a date code on the engine side flange, year and month.
B=1946 etc

Here is the damper type that is in my 1950 Mark V, which has aluminum dashpot pistons.

This is the only kind I have ever seen before now, so apparently yours is some earlier version. Are your pistons aluminum or brass?
My '38 SS has brass pistons and no damper stems.

Hey, Rob, I represent that remark! :grin:

Hopefully someone can help Richard solve this carburettor mystery? I’ve seen that kind of damper before a long time ago but, sadly, I can’t remember just where? “Riley” keeps popping up in my memory.

Would there be any reason why a ‘standard’ SU damper of the same length with a ventilated brass top not work?


SU had a lot of customers, certainly Riley among many. The jet linkage says to me MG manual choke.

We need to work out what model carbs they are. The parts to convert back to original type jets are available. The early damper may not have been quite as good. A later damper should be fine if it is submerged in oil for the full stroke. It may be that they should not have dampers?

How do they work without dampers?

I did think of MG as well but they were generally 1 1/2" SU’s whereas I thought that the 3.5L had
1 3/4"?


Thanks! The auxiliary carb is still blank after reading some of the suggestions here but not sure this choke system works either- the engine dies if opened so could go back to a fixed jet
Also I bought the needles for a 3.5 jaguar and who knows what the jet is? Engine starts ok but runs very rich anyway but early days - the test drive total is about 4 miles with a few hours of garage idling/ running in after standing so long
The carb piston is brass and has the hollow shaft (and the intact side working)
The SU people are making something that will work- the length being the issue apparently but if someone has pulled apart and repaired would give some idea before I attack the working one

Hello Richard,

I’d try and find a set of the correct SU carburettors for the car and sell the ones you have to offset the cost. You’ll be much happier. Alternatively, you could reinstate the fixed jet and the starting carburettor parts but that will be a pain.



I think it’s true to say that the MkV 3.5 litre has the damper and the MkV 2.5 litre and earlier cars of either size don’t.

The 3.5 engine should have the SU H4 model 1-1/2" throat measured on the engine side (the air cleaner side is a bit smaller).
Needle DY
My Haynes SU manual says there were 3 jet sizes, .090", .100" & .125", and DY is listed among needles for the .090" jet.

It looks like they might be the right bodies and piston chambers, but perhaps other parts have been changed by somebody wanting to have manual chokes instead of the starting carb. Look for numbers on the bodies.

My '38 SS 1-3/8" H3 carbs with brass pistons have solid shafts so could not have a damper.
It was my understanding that brass pistons being heavier did not need the damper, but aluminum pistons pop up too quick on acceleration unless you have the dampers.

My picture above is of a Jan '56 MGA 1500 with 1-1/2" H4 carbs, though a newer version with additional air ports.

Thanks- my Jaguar autobook one 1946-48 says the 3.5l has dampers, the 2.5l a cap only and the aluminium piston models have springs as well
Peter Scott blow up picture of the carbs shows the brass damper with solid brass piston like the ones in my car
Going to knock the pins out of the other to try see what the valve looks like to see if can get one made

I didn’t think to look in the MKV Parts Catalogue and it shows the type of dampers Richard has. There is a cross-section of a carburettor in the MKIV Service Manual which shows the damper with a ball and spring.

Interestingly, the Service Manual says that the 1 1/2L and the 3 1/2L have hydraulic dampers whereas the 2 1/2L doesn’t. I wonder why that might have been?

As always I learn something else thanks to you knowledgeable fellows! I don’t know why I assumed that they were 1 3/4"?

That’s the best plan now that you know they are the correct carburettors. Apologies for my ignorance. I bet that the Otter Switch in the water rail will probably be okay so you could reinstate the Starting Carburettor.


On the XK120 and Mark VII engines they are 1-3/4" model H6.
I also learned something, did not know the 1-1/2 Liter was manual choke.

Excellent- so it is only a ball bearing type valve! I can fix this :blush:

Is one of the dampers complete? Can it be disassembled to see what’s in it? I’d love to see what it looks like on the inside.


Can confirm a 3 mm ball bearing fits into the 1/4 inch hole in damper piston with enough clearance to perform valve action

Excellent, Richard!

Now all you have to do is convert the carburettors to a fixed jet set-up with the Auxiliary Starting Carburettor. Someone will have the correct solenoid.