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 followed in the late 1950s and became the most widely fitted SU carburettor of all. 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 Cooper, MG Midget, Austin-Healey Sprite, Triumph Spitfire and Morris 1100, among many others.
- HS4 — 1½ inch bore. Fitted in pairs to the MGB, and to many BMC saloons and some Austin-Healey 3000s.
- HS6 — 1¾ inch bore. Used on the Triumph TR3 and TR4, MGC, Austin 1800 and Rover P6 2000, among others.
- HS8 — 2 inch bore. Used on larger engines such as the early Jaguar XJ6 and Rover 2000 TC.
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 — 38mm (about 1½ inch) bore. Used on later Minis and Metros.
- HIF44 — 44mm (about 1¾ inch) bore. Fitted to the Metro, Maestro, Montego and V8 Range Rover, among others.
- HIF4, HIF6 and HIF7 — earlier HIF types named in the old notation, for example twin HIF4 on later MGBs and twin HIF7 on the Jaguar XJ6 4.2.
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, H6, HIF44 or HIF6
- 2 inch (51mm) — HS8 or H8
Reading the Carburettor Identification Stamp
Most SU carburettors carry a specification number on a small aluminium tag held under one of the suction chamber screws. It will read something like AUD 135, AUC 946 or FZX 1049. A letter on the end, such as F or R, marks the front or rear carburettor of a pair.
The prefix letters are part of the SU part number series. AUC and AUD numbers are typical of earlier carburettors, and FZX numbers of later HIF and replacement carburettors.
The number cross-references to the original vehicle application. Type it into Find My Kit to see the exact specification and every service part that fits.
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 and Triumph TR range — were fitted with twin SU carburettors, and some, such as the E-Type Jaguar, had three. They are matched sets of the same type (for example twin HS4 on the MGB). 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. You can look up your car in Find My Kit, which lists the original SU specification for thousands of 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 SU parts, or get in touch if you need guidance.