Bentley MARK VI 1947 Service Manual – Air Cleaner & Carburetor Specs

You’ve got a Bentley Mark VI on the lift, maybe an ‘A’ series with that odd air cleaner setup, and the carburetor’s running lean. You dig through your pile of reprint manuals and find nothing on jet needle specifications. That’s where the Bentley MARK VI 1947 Service Manual comes in. This isn’t a reprint; it’s the actual factory service bulletin from Bentley Motors, dated 1947, covering two critical bulletins: BB-20 on air cleaner differences and BB-45 on the oil bath air cleaner retrofit. 44 pages of direct-from-the-factory data. No guesswork. You get the exact carburetter jet needle types (LB1 or SC), the chassis numbers affected, and the step-by-step procedure for modifying carburetors when switching to the optional oil bath cleaner. Without this manual, you’d be chasing a flat spot or a rough idle for hours – or worse, using the wrong needle and damaging the engine.

44 pages. That’s it. But those pages carry the authority of Bentley Motors (1931) Ltd., printed in England in 1947. Every spec is original OEM – no aftermarket guesswork.

Air Cleaner Differences: A and B Series

Bulletin BB-20 spells out the difference between the Bentley-manufactured air cleaner on ‘A’ series chassis (B-AK, B-AJ) and the A.C. cleaner on ‘B’ series (B-EH, B-BG onwards). The manual lists exactly which S.U. carburetter jet needles to use: type LB1 for Bentley cleaner, type SC for A.C. cleaner. If you swap cleaners, you must change the needles. The identification marks are stamped on the head of the jet needle. That’s the kind of specific data you won’t find in a generic manual. For more on chassis identification, refer to Bentley Mark VI Service Manual Bulletin BB-13.

Oil Bath Air Cleaner Retrofit: Factory Procedure

Bulletin BB-45 covers the optional oil bath air cleaner. It’s not a bolt-on; the manual explains why the higher filtration protects the engine in dusty conditions and mandates carburettor modification to maintain correct fuel/air ratio. The procedure spans pages 2 to 6 of this manual. It tells you to modify each carburettor separately to avoid mixing up components. Parts list included. This is the original factory retrofit procedure, not some aftermarket hack. If you’re restoring a Bentley for desert use, this bulletin is essential. Related heater system details are in Bentley MARK VI Service Manual Car Heater System.

What Carburetor Jet Needles Does This Manual Specify?

Two types: LB1 and SC. The manual gives the exact chassis ranges. If you’re running an ‘A’ series with a replacement A.C. cleaner, you need to swap to SC needles. The manual even shows where the part number is stamped (on the head of the plain portion that locates in the air valve). Without this manual, you’d be guessing jet sizes and chasing a misfire. For an overview of the broader automotive restoration landscape, see Automotive Industry Overview.

Trust the Factory Service Bulletin Over Reprints

This is not a third-party reprint. It’s an original Bentley Motors service bulletin printed in England in 1947. The document is a scanned copy of the actual bulletin, complete with figures showing the air cleaners. Reprints often blur photos or transpose numbers. Not here. You get the exact specifications as released by the manufacturer. For additional context on vintage car restoration standards, Automotive Industry Overview is a useful reference.

3 Key Specifications from the 44-Page Manual

• Air cleaner types: Bentley manufacture (fig.1) vs A.C. manufacture (fig.2) – different air flow characteristics
• Carburetter jet needles: LB1 for Bentley cleaner, SC for A.C. cleaner – stamped identification on needle head
• Oil bath cleaner modification: separate carburettor work, parts list, and procedure to counteract air flow change

Who needs this manual? Anyone working on a 1947–1948 Bentley Mark VI with S.U. carburetors – especially if you’re swapping air cleaners or dealing with an oil bath retrofit. Car restorers, specialist shops, and serious DIYers will find the factory specs invaluable. The manual is the complete OEM reference for these two bulletins. For the full manual set including bulletins BB-13 and BB-45, check Bentley Mark VI 1947 Service Manual.

Does this manual cover the entire Bentley Mark VI?

No. It covers two specific service bulletins on air cleaners and carburation.

What years and models does it apply to?

The bulletins are dated October 1947 (BB-20) and April 1948 (BB-45). They apply to Bentley Mark VI ‘A’ series (chassis B-AK, B-AJ) and ‘B’ series (B-EH, B-BG onward). If you have a later Mark VI, the oil bath cleaner retrofit still applies, but verify chassis number. The manual does not cover engine overhaul, brakes, or electrical systems. It is strictly focused on air cleaner identification and the optional oil bath modification. For a broader set of bulletins, see Bentley Mark VI 1947 Service Manual and Bentley MARK VI Service Manual Car Heater System.

If you’re restoring a Bentley Mark VI or just need to get the carburetion right after swapping air cleaners, you need the factory data. Download the Factory Manual from AutoRepairManuals and get the exact specs that kept these cars on the road in 1947.