Preferred SU ?

[Bob Culver]

A simple plate with countersunk screws suffices for the adaptor and keeps the SU closer to engine, allowing room for a filter. The horizontal carbs look more period.
Considering how restricted the manifold is, the improvemnt with SU is surprisng. Curiously,  I found to modest revs, and without experimenting with the needles, a larger manifold seemed of no advantage, although was adopted for the sports models.

[Tony Press]

The 1928 Chummy and 1929 Standard Sports both have 1 1/8" SU's from a post war Morris with weighted pistons (no spring) - mounted on 1936 manifolds with adapter plates. Sorry I don't have needle details but both work well (Wednesday I had the Chummy cruising at 48 mph in 32 degree temperature, but unfortunately couldn't turn the eater off !  )  .

The Sports has an electric SU type pump which works well, the Chummy has gravity feed needing a full tank (down to 1 1/2 gallons) for reliable fuel feed.

[jansens]

This may be useful for identifying old SU carbs: https://www.mgexp.com/phile/71/223105/SU...4789_J.PDF

It lists cars by make and model then what SU was fitted as standard, the needles and springs and the SU parts number going back to the late 20s it seems.

As far as I can tell the 1 inch OM carbs are the ones with the suction chamber mounting holes aligned on the bore of the carb throat (the first picture in Douglas' post). The pre-war Morris carbs seem to be UBA type that have the two holes for mounting the top at right angles to the throat.

I recently found two of those at a wreckers here that I am rebuilding to use on my Riley 9 (slightly bigger would be better but these will run). I think the other, similarly sized carb, is the HV1 but I have never seen one and am not sure what the difference between that and a UBA is.

It's worth noting that with the HV series the 'usual' SU carb number pattern where the number is the number of 1/8 increments over 1 inch doesn't work. So a HV1 has a 1 inch throat unlike the other H series carbs which would be 1-1/8th I think.

The OM, UBA and HV1 use the same rebuild kit. I actually found I could get those cheaper (and some other parts like the damper caps - no actual damper but a vented cap) from the Pre-War Morris club than from Burlen. Refreshingly you don't seem to need to be a member to buy parts from them. Well, they charged my card at least, hopefully the parts arrive!

Simon

[Douglas Alderson]

Hi Simon

If you contact Burlen www.burlen.co.uk you should be able to get one of there SU Parts & Specification Catalogues which in addition to the info in the link you posted also has all the parts they produce etc.

Having checked the carbs in the photos I posted I belive they are are as follows.

1 photo OM 1” which appears to fit the manifold with the holes aligned
2 photo HV2 1 1/8” which need the holes adjusted to fit well also the manifold was enlarged
3 photo H2 1 1/4 with adaptor 

Re the dates if you want a period carb then they are dated as follows

1929 HV type introduced
1931 OM type introduced
1937 H type introduced 
1958 HS type introduced 

The size measured on engine side of the carb they are available as follows

1” OM and HV1
1 1/8” H1, HV2
1 1/4” H2, HV3, HS2

The OM HV and H are hard to find, but HS2 are very common.

The above covers I believe the most common types on A7’s.

[Bob Culver]

This was all thrashed out some years ago but I do not have the reference. A complication is the lack of written designation on the parts and the interchangeability of the tops; ie dashpot or not. Only the output dia seems to differ between the 1 inch and 1 1/8 inch and on stock non sport cars the piston seems to seldom or ever lift fully so any performance difference unlikley, although a small outlet gives a more progressive throttle. Later semi downdraught look wrong on a 1930s car.  Note that when comppring needle shapes only the diameters in range of lift are invoved in normal running. I only have experience of the 1 1/8 dashpot on a mildly altered RP. Seemed surprisingly beneficial ; much as the 1937 head. And car could be driven very smoothly in downtown traffic crawls as applied before the stop go sprints associated a myriad traffic lights.

[Ian McGowan]

Having been there and done that, absolutely correct Douglas.

[jansens]

Thanks Douglas, they don't have a price on the catalogue on their site so maybe they give it to you free if you do an order for parts and ask for it (I doubt it!)? I did find copies online though. The exploded diagrams are very handy.

Simon

[Jeff Taylor]

Simon,

On Burlen's site it says "Please note: This item is limited to 1 per order" - presumably meaning when placing an order for parts though that's not entirely clear. I bought my copy back in 2003 direct from Burlen and the cover price then was £9.95p.


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[Tony Press]

Or if you really want to get the complete story purchase the book 'Skinner's Union' from Burlen - this gives the full history of the company and details of every carburettor.

Possibly you might be able  to buy a second hand copy via ABE booksearch by now ?

[Douglas Alderson]

If you go to an event Burlen are at the catalogue is free they also have one for Zenith.