Fitting 2" HS8 SU Carburetors and manual choke to 1965 "S" Type 3.4 litre.
(also applicable to models : 3.4 Mk1, 3.4 and 3.8 Mk2, 420, * XJ6 Series 1 and 2)
A brief account of what is required.
At the time of restoration in 1996 I made a decision to change from the standard 1.75" HD6 SU carburetors to the later 2" HD8 version, the reasons being:-
1. Original carburetors had deteriorated to a point beyond economic repair.
2. HD8 2" is easier to repair, maintain and set up (in my opinion)
3. Improvement in performance (I hoped!)
4. Lack of annoying electrically operated thermo starting carburetor (AED on later models).
5. More economic on fuel.
Obtaining 1974 Series 2 XJ6 2" SU's was no problem as they are readily available and will bolt straight onto the existing inlet manifold as fitted to all Mk 1/2, 420 and "S" Type models with either the 3.4 or 3.8 and in the case of the 420 models, 4.2 litre engines. Minor chamfering of the inlet port apertures is recommended to give a smoother gas flow and new gaskets need to be fitted. Each carburetor will need to be stripped for cleaning, checking of float levels and wear. Overhaul kits can be obtained again from Burlen Fuel and are easy to fit. Burlen also sell at nominal cost an SU parts guide and a detailed pictorial repair manual.
The HS8 Carburetors are not fitted with Jet diaphragms like the HD6 and HD8 but do have self centering spring loaded needles. The jets are 100 thou diameter as opposed to the HD's 125 thou. This does not pose a problem however as there is a wide range of 100 thou needles available from Burlen Fuel.
Removal of the Enrichment device from the HS8 is a simple matter and the purchase of the following components from Burlen will enable you to convert to a manual choke on either one or both carbs at a cost much less than that quoted by many parts suppliers. For Burlen Fuel web site see links page on this web site by clicking on Links button when you return to the Home page.
Item. Part No Cost (approx in 2001) Quantity required
1. Link rod and levers (kit) WZX 871 £8 1
2. Pivot bolts AUC 1426 £8 2
3. Choke cable Auto Accessory shop £5 1
4. Gaskets AUC 1285 £2 2
5. Gaskets AUD 4866 £2 2
Total Cost £26 +VAT
After installation, and after finding a convenient (hidden) place for the choke cable and knob, the carburetors will need to be synchronized and adjusted for the correct fuel air mixture. Needle profile selection may also need to be addressed.
I Started off using BCE needles but found these were too rich and not giving the best performance so have now installed BAW profile needles. For performance reasons, the use of an original air cleaner is recommended. Note: - If using twin 2" HS8 carburetors then you will also require a 420 inlet horn as the original one for the 1.75" SU's is too small.
A useful book written by Des Hammill , "How to Power tune Jaguar XK 3.4, 3.8 and 4.2 engines" is available from Veloce Publishing PLC (Web site is www.veloce.co.uk) price £14.99. This deals with all aspects of engine tuning and includes an in depth section on carburation. Burlen also supply a small booklet listing all available needles and jets.
Click once on picture below to see installation in my car.
Carburetors and choke set up with non standard air cleaners later replaced with standard air cleaner.
Good luck with the conversion. If you need more information you can always email me, phone or ask when you see me.
* Note: Series 1 and 2 XJ6 models are already fitted with 2 x 2" HS8 SU carburetors but the manual choke conversion gets rid of the troublesome AED starting carburetor.
Colin Murray. (Email) Return to Technical Page