HV2 carbs, identification help

Hi, I’ve been asked to help someone with an ERA. I think the carbs are SU HV2, but I’m not sure. If there is a group here on JL where someone might be able to help me identify these carbs, then this has got to be it.

Could someone post a pic, or tell me where to look for any identifying marks or features?

Here are some pics of what is on the car:

Hi Andrew,

That looks like serious stuff but if you have carb problems then I’m
sure Burlen will be able to help.

What’s the problem?

Kind regards,


Andrew Waugh wrote:

The photos show what look like HV carbs to me. The number following the “HV” indicates how many 1/8" increments the inlet diameter is over the base 1" diameter. This can be determined by measurement on the inlet. HV2 would be 1.25 inch diameter. SU (Skinners Union) business is handled directly by Burlen these days. There also are other good vendors for parts and repairs.

Thanks guys.

I know about Burlen. What I was trying to do was confirm that they really are HVs.

The mech that serviced and sold the car to the new owner claims that the carbs are shot and can’t be saved. The pistons aren’t at the same height (even with the engine not running). Before I start taking them apart in the least, I want to be sure that they are HVs, then I can contact Burlen about spares, then I will pick up a wrench/screwdriver.

1 Like

I’m not sure an ERA would be running carbies that small. I would have thought that now they would be 2 3/8" or 2 1/2".
They look right for pre war , the early ones had " Adderley park" cast intot he float bowl tops . And had the bull nose shape where the thimble filter sits.
They certainly look like HV type. The rule of the number being related to size is almost always true. There is one exception [ which I’ve forgotten]
] I had a chart given me by the local manufacturer of SU carbs which showed it but lost in my " filing system"

This is the sort of carbie I would expect to see on an ERA. 2 1/2 ", twin or single float bowls , choice of aluminium or Magnesium.
Burlen claim all there products are made in UK . And used to show [ possibly still do] these carburretters in their brochure. OBvious not UK made as this picture was taken in Melbourne where they were made of a parially made e xample The dark colouration results from those parts being Magnesium and oxidising quickly… These are serious looking carbies and put H 8s to shame . But really only of value for highly tuned cars running alcohol based fuels.


I’ve no idea if these are the original carbs, nor even if the engine has been modified. Without having taken anything apart, or measured anything at all, they appear to be smaller than HD6s, and the (filterless) intakes seem a bit on the small side. Burlen lists the carbs for various Riley engines of that era (and the owner says it is a Riley engine).

I’m just trying to get clear on if they really are HV carbs before I go much further.

Thanks for the info.

Perhaps we should start with identifying which Riely engine it is , then from that see if the carbie s are correct

If you have some more complete pics of the engine , there are a number of pre war Riley owners here in the VSCC including one who is the maker of SU carbs, They could probably be more definitive.
Riley had a number of models pre war…

That is indeed what I was thinking. I can sort of claim to know about leading the life of Riley, but not much about he looks. Is there some easy way to distinguish one Riley engine from another, so that I can tell what to take pictures of?

Joe Curto, the American SU carb specialist, maintains a photo library on his website detailing numerous types of SU carbs. There are examples of HV2 and HV3 carbs.

Thanks Mike for the Curto website, lots of good pictures there, click on one and you get more.

Google found these pictures of Riley engines.

But to add to the confusion there was a George Riley building sprint car engines in northern California in the '30s.

Here is some stuff about ERAs.
According to this, there is only one that has ceased to exist, a pretty good record.

Percy Riley may have been a very distant relative, assuming we’re both descended from Raelleagh, but he didn’t leave his money to me.
As to the life of Reilly, I’ve tried it and so far it is great, and even more so being retired. I used to hear about the TV show when I was a kid but never saw it until it came out on DVD. Its about a machinist making airplane engines.

On looking up HV carbs in the SU Workshop Manual, I find they are sized 1/8" different from what I wrote above. Also, if you are not sure about carb/engine combination you can estimate which carb is correct for a specific engine if you know the maximum horsepower for the engine. Maximum horsepower is rule-of-thumb constrained by how much air can be fed into the engine. A carb which limits airflow below engine capability will constrict performance. A carb with much more airflow capability than an engine won’t give dramatic horsepower increases.

SU rates the HV by (throttle diameter, max. capacity) as follows:
HV.1 (1 inch, 27 hp)
HV.2 (1.125, 35)
HV.3 (1.25, 45)
HV.4 (1.375, 55)

The H and HD carbs have similar horsepower ratings for similar throttle diameters but their number ordering is one eighth inch shifted from these HV numbers (H3 is 1.375 inch, 55 hp).

As an example, an engine with 125 horsepower maximum would need two H4 carbs at 1.5 inch throttle diameter and 65 horsepower rating each. Throwing H6 carbs on such an engine would not yield bolide performance without providing for major increase in engine breathing capability.

I wonder whether the prefix HV was used pre war . A bit like the terms Mk IV , Mk I , as at the time there weren’t the later type to differentiate from .

Looking at the pictures , he may consider new float bowls as it seems the one shown has stripped the thread for the stud in the bottom and had it replaced with a bolt.

As he has the nice old Adderley Park float bowl tops , he may find the article I did in CJA mag on how to retain and use them if the banjo bolt thread has stripped , useful.
Rob is right about larger carbs, But on my current 3 1/2 engine I had the inlet ports opened out , [ not in a circular manner as that would impinge on the push rod holes , ] but in an oblong manner

MGB rockers give 3/8" valve lift , and iskendarian valve springs allow for the extra lift with out becoming coil bound. Matching the ex ports on head and manifolds is also a big help
AS the 1 13/4" SU have a 4 bolt mounting I made alloy adaptor plates which replace the original spacers. And use MK IV float bowls and choke on early XK 120 1 3/4" carb bodies.

It has made a noticeable difference without being obvious to look at .

Maybe HV means Horizontal Venturi?
There was also a vertical venturi made by SU, used I believe on the early OHV 1.5 Litre cars with engines K1 through K1200.


Would that make HD carbs , downdraft?: >)

And MG TCs had semi-down draft carbs

The downdraft carbs weren’t a great success as the damper was resting on the side of the chamber.

I couldn’t find where the downdraft or vertical venturi ever had a letter designation.
HD is Horizontal with Diaphragm
HS is Horizontal with Seals
HIF is Horizontal with Integral Float chamber

Here is one for a 1937 Rover, probably pretty similar to whatever was on the early SS 1.5 Litres.
Notice the oil cup on the dome neck, because the piston inner shaft slides on the inner bore just like our side draft models.

And one I hadn’t seen before, a sloped piston.
I can’t imagine what would be the reasoning here, unless it was bonnet clearance.

1 Like

I don’t think the slopes carbies were because of height issues ,The old WOBentleys had plenty of clearance under the bonnet.

The downdraft carbies… Prewar the SUs relied on the weight of the brass damper,and postwar, SU found that alloy dampers were cheaper to make but needed a spring to compensate for being lighter.
The downdraft didn’t have this gravitational assist.

The Rover Carbies shown have post war float bowl tops , the overflow tubes are a sensible mod, but one has to be careful about mix&matching as the mounting point for the two types are incompatible .

I have finally remember one of the examples where the rule about SU type numbers doesn’t match the size.

The HV8s are actually only 1 7/8"

Many years ago SU were owned by BMC who realised that production cars were moving to fuel injection and decided to sell off SU.

Included was a museum of all the old types they had made and H8s and parts there of.
The gentleman here in Sydney, knew all this and wanted the lot . So while the locals were hoping for some cheap cherry picked bargains , he made a killer bid for the lot, and got it.
There were protests that this historic collection should not be allowed to leave UK. But by the time they got round to making representations , it was on the boat and bound for Australia.
So H8 s were sold from parts in the stock and when parts ran out more were made out here.
And the range expanded to include the 2" to 2 1/2" carbies .
The maker here in Melbourne basically started because an ERA owner asked him to copy on of the big SUs used on the ERAs.

Which is sort of where this subject started.

I have recently been researching SU carbs and those pictured are OM1 carbs as far as I can determine. The differentiator is that the vacuum chamber has the mounting screws in parallel to the carb body. From what I have seen, all the HV and H series carbs of the 1" to 1 1/4" have vacuum chamber screws perpendicular to the body. As Roger McWilliams pointed out, the HV series seems to be 1/8" off from the H Series carbs. The OM1 should be 1" at the throttle plate as is the HV1. The HV2 and H1 will both be 1 1/8", the HV3 and H2 will be 1 1/4", etc.

Perhaps Andrew is reading this, from his workbench, up in Valhalla!

I miss that guy…

1 Like


Unfortunately not that simple.
WE all are aware that H and HD series carburetters have their suffix number directly related to the Throttle Diameter (1 inch plus suffix number x 1/8in)
But there is no such direct relationship with HV, OM or D series carburetters.
My best assessment is suffix number is simply an indication of ascending number denotes ascending size, and maybe with a couple numbers approximating actual throttle diameter was the motivation to formalise a direct relationship with H series carburetters?

HV0 = 7/8" throttle diameter
HV1 = 1"
HV2 = 1-1/8"
HV3 = 1-1/4"
HV4 = 1-3/8"
HV5 = 1-5/8"
HV8 = 1-7/8"

My SU listings say there was no HV6 nor HV7, and indeed H0 and H1 are noted as ‘Special Order Only’

While the visual carby reference of pics is vey useful, it would b e a mistake to take it as an infallible reference
The 2 1/2 Jaguar carbies for example are showna bronze bodies without a flange for air cleaners. I did see a pic of an protorype engine in the factory being tested with barbsof this type. although B&W don’t allow us to see whether alloy or bronze. But The 2 1/2 SS carbies I have and have seen have air cleaner flanges. Even SS 100s that did not have air cleaners had the carbies with flanges And these are very early cars, one being the 4th SS100 built. Some shown also have post war float bowl tops.
And the 3 1/2 litre SS 100 arbs are shown as being basically MK IV carbs, Although both are missing the fitting to be operated by the hand throttle.
The thing that has puzzled me , is why SS100s , with the same engine as saloons had ’ beer bottle’ suction chamber tops but saloons had conventional
herwith contemporray pic of a 3 1/2 SS100 showing the carbies

John Clucas 3 1/2 SS among others has this type , but a further issue arises. John’s car came with 1 5/8" SUs. Sodid d saloon have the smaller 1 1/2" carbs and the beer bottle top crabs were 1 5/8’ on the 100. Were the head ports enlarged for this
It’s not as if one can just blt on the bigger cars as the ports , once in a little become rectagular, so enlargement is hand work. not just a boring head { Rectangular to clear the pushrods.]
I spoke to the bloke who made slopers for Burlen… He will look up his books about slopers but he’s a year older than me, it’s forecast to be 43-44C today and neithe r of us can be dragged away from the air con.