HS2, HS4, HIF44 — What Have You Got?
If you're working on a classic British car, chances are it's fitted with an SU carburettor. SU (Skinners Union) carburettors were fitted to millions of vehicles from the 1930s through to the 1990s — from the humble Mini to the Jaguar E-Type — and understanding exactly which type you have is the essential first step before ordering any parts.
This guide will walk you through how to identify your SU carburettor by type, size, and application.
The SU Carburettor Family
SU produced several families of carburettor over the decades. The two main types you'll encounter on post-war British classics are the H/HS series and the HIF series.
H and HS Series
The H series was the original SU design, introduced in the 1930s. The HS (H-Series Improved) followed in the 1950s and became the most widely fitted SU carburettor of all time. Both use a separate float chamber mounted to the side of the body.
Common HS variants include:
- HS2 — 1¼ inch bore. Found on the Mini, early MGB, Triumph Spitfire, Triumph Herald, and many others.
- HS4 — 1½ inch bore. Fitted to the MGB (later models), Triumph TR4/TR5/TR6, Austin-Healey 3000, Jaguar XK engines, and more.
- HS6 — 1¾ inch bore. Used on larger-capacity engines including Jaguar V12 applications and some Triumph six-cylinders.
- HS8 — 2 inch bore. Rarer, used on high-performance and larger displacement engines.
HIF Series
The HIF (Horizontal Integral Float) series was introduced in the 1970s as a development of the HS. The key difference is that the float chamber is integrated into the body of the carburettor, rather than being a separate unit mounted to the side. This made the HIF more compact and improved fuel delivery consistency.
Common HIF variants include:
- HIF38 — 1½ inch bore (38mm). Used on later Minis, Metro, Allegro.
- HIF44 — 1¾ inch bore (44mm). Fitted to later MGB, TR7, Rover SD1, and a wide range of British Leyland vehicles from the late 1970s onwards.
- HIF6 — 1¾ inch bore. Earlier HIF variant found on some Triumph applications.
How to Identify Your Carburettor by Size
The simplest way to identify an SU carburettor is to measure the bore — the internal diameter of the intake throat. Remove the air filter and look straight down the carburettor. With a ruler or vernier caliper, measure across the opening:
- 1¼ inch (32mm) — HS2 or H2
- 1½ inch (38mm) — HS4, H4, or HIF38
- 1¾ inch (44mm) — HS6, HIF44, or HIF6
- 2 inch (51mm) — HS8 or H8
Reading the Carburettor Identification Stamp
Every SU carburettor has a type number stamped into the body, usually found on a flat machined face on the carburettor body itself, or on a small tag. The stamp will read something like AUD 135F, AUC 2340, or AED 1067.
The prefix letters indicate the type and application:
- AUD / AUC / AUE — Standard production carburettors
- GHD / GSH / GHS — Genuine Heritage (replacement) parts with original specification
The number itself cross-references to the original vehicle application. If you have the number, you can use it to look up the exact specification and find matching service parts.
Distinguishing HS from HIF at a Glance
Once you know what to look for, telling an HS from an HIF is straightforward:
- HS series: The float chamber is a separate cylindrical unit bolted to the side of the main body, connected by a short fuel passage. The carburettor looks wider overall.
- HIF series: The carburettor body is a single compact unit with no separate float chamber. It looks more self-contained and is generally slightly smaller overall.
Twin Carburettor Setups
Many performance British classics — the MGB, Austin-Healey 3000, Triumph TR range, and E-Type Jaguar — were fitted with twin SU carburettors. In most cases, these are matched pairs of the same type (usually twin HS4 or twin HS6). When servicing a twin setup, it's important to treat the carburettors as a pair and replace wear items on both at the same time to keep the engine in balance.
Not Sure? Check Your Vehicle
If you're still unsure which carburettor you have, the quickest route is to cross-reference against your vehicle's original specification. The carburettor type is listed in workshop manuals, and we've put together a detailed FAQ covering the most common vehicles. You can also contact us directly — we've been supplying SU parts for decades and can identify your carburettor from a description or photo.
Once you know what you have, finding the right service parts, repair kits, and replacement components is straightforward. Browse our full range of genuine Burlen-manufactured SU parts, or get in touch if you need guidance.