I had all three of my carbs rebuilt last year by:
28f High St, Leighton Buzzard, LU7 1EA, Tel 01525 371369
They did an excellent job and the cost was £250-300 for all three – not cheap but kit now like new. They quoted 6-12 weeks for work to be done.
Ed. Extract of services provided pasted below as taken from their website Oct 2013
Over the past 80 years or so there have been innumerable carburetter designs by many different manufacturers, and it would be impossible for us to compile a detailed rebuild procedure for each one. However, all carburetters tend to follow the same principles of design, enabling us to give an indication of the various processes involved.
- Carburetters are completely stripped.
- Components are subjected to a four part chemical cleaning process which is the only effective way to remove dirt and corrosion from the internal circuitry as well as restoring the castings to their original appearance.
- Castings are polished to a high standard, or stove enamelled. *
- Mating faces are re-machined to ensure flatness.
- The throttle spindle housing is re-bushed using P.T.F.E. lined glacier type bushes and line reamed to correct tolerance.
- Steel components are de-rusted and inhibited.
- Steel components are re-plated. *
- Brass components are chemically brightened.
- Brass components are polished. *
* Denotes concours service only.
Carburetters are now re-assembled using all new wearing components, i.e.:
- Throttle spindle
- Float needle valve
- Throttle plate
- Volume/Air screw
- Throttle plate screws
- Metering needle
- Seals and washers
- Jet Ancillaries
Any other components found to be faulty will be replaced. All internal components are adjusted and set as per manufacturer’s specification. Carburetters are then engine tested to ensure correct functioning of the following:-
Fuel level, Idle circuit, Choke mechanism, By-pass circuit, Pull down and fast-idle operation, Progression circuit, Correct throttle operation, Main circuit, Correct response to mixture adjustment, Pump circuit.
(Upon re-fitting to vehicle, normal adjustments will be necessary)
Carburetters are given a final inspection and guaranteed for 12 months.
The Chrysler 360 Rotomaster turbocharged version fitted to about 30 Beaufighters and 25 Brigands apparently has a major flaw in engine control systems as originally configured and supplied by Bristol and Rotomaster. The flaw is with ignition timing which needs to be massively retarded under boost conditions, and the set up originally supplied by Bristol is very hit and miss. If the ignition is not retarded quickly enough by the distributor set up then you get massive detonation.
Any turbo charged car maintained by Bristols or where the owner has taken advice from them will have been fitted with a MSD Ignition system (part number MSD 6BTM) which is controlled by a MSD control knob (part number 6BTM 6462). The control knob allows the user to dial in the extent of retard under boost conditions from NIL to 3 degrees per pound of boost pressure. Once set up correctly the knob is best hidden, at least from a retard like me. You will of course appreciate why straightaway! The exact set up depends on fuel quality used and the set up of the turbo wastegate.
Below are copies of the instruction manuals. Please click the appropriate heading to download a copy.
Worn butterfly spindles are sometimes the cause of erratic and unstable tick-overs. Replacement spindles and re-bushed bodies seem to be the only cure. Even then it becomes a good policy to blank off the non linkage end of the housing with a brass turned cup tapped home. To provide an air tight seal the linkage face may be sealed with a thin small diameter ‘0’ ring.
When the butterfly is in the closed condition, the mixture signal will be improved via the mixture screw. Also any fuel dribbling down the choke tube will not leak out via the spindles resulting in a much cleaner carburettor.
When a hot engine is switched off there is a sudden heat rise into the carburettors. This causes the fuel to boil which expands and is now forced up the emulsion tube then down to the butter fly hence leaking fuel out of worn spindles. Heat rise has always been a problem with all Bristol engines, 6 cylinder and V8s. ‘Tufnel’ or ‘Packsalin’ insulation plates provide an excellent barrier to this heat rise. The main body, on later V8s, was even made from ‘phenolic resin’ in an attempt to prevent this heat rise. These insulation plates are 0.062” or 1.5mm thick with the required gaskets. One is fitted direct to the head with a gasket top and bottom and then the fulcrum bracket is put on, a further green gasket, then the second insulation plate and then the grey gasket, finally the carburettor. When fitting the carburettor assembly to the head, do not forget the mounting flanges must be flat. Do not over tighten the thin retaining nuts, they can warp the flanges.
Note, the information in the handbook or workshop manual is only correct at the time when it was written. It does not apply now ie the jet sizes quoted are for standard engines on 82-3 octane fuel. Most engines are not standard by any means so, with heads that have been skimmed and distributors that are no longer accurate, engines will not be giving their best power. For an incremental rise in compression so must a change in the size in jets be considered.
Consider one 320cc cylinder using 83 octane fuel, the compression could be 8.5: l. For the same cylinder with a refurbished head that may have been skimmed and now running on 93-5 octane fuel, the compression could be as much as 10:1. What you really need to know is the clearance volume in the cylinder head to determine the compression ratio. This is when you need to look at your jet sizes. I know this is not easy, in fact it took BCL some time to finalise these settings. A word of warning; if receiving any rebuilt carburettors, strip and carefully reassemble them yourself. This was always done at BCL. It has been known for carburettors to arrive with different needle valves in one to another, different thickness washers one to another, throttle plates not centralised, etc. The choke plate will require lapping if it is to function at its best.
Also remember that fuel density is dependant on its temperature so the hotter the fuel the weaker the mixture. Remember, on fuel injected cars, fuel is in constant circulation in an effort to maintain this density.
Fuel pump pressure. Ex works, fuel pumps were always stripped and adjusted before fitting. Make sure yours is right, 2psi is about right. How? Drill and tap the front banjo bolt, fit screwed tube, connect to a sensitive low pressure gauge and observe the pressure reading, adjust the large fuel pump spring until correct. Remove the screwed tube and replace with a blanking bolt.
Starting from cold, the load on the starter motor and battery can be eased considerably by fitting an electric fuel pump. An ordinary SU fuel pump fitted in the fuel line with a manual electric switch with a warning light should ease this problem. How? From the delivery side of the fuel tap take a flexible pipe to the inlet side of the SU pump, from delivery side of the pump connect to the inlet side of the AC mechanical pump. Now just switch on then wait for the SU pump to stop ticking, switch off – instant engine start. Why? Carburettor float bowls are full and ready to go. Before with float bowls nearly empty it took a little while for them to fill. This is why a priming leaver is fitted to the AC pump.
Whatever fuel you use or condition your engine is in, the ignition must be adjusted accordingly. Marks on flywheels, or bits of metal and marked front pulleys are of very little use in this changed situation; usually a slight retarding is required. Remember your distributor was recommended for replacement at 40,000 miles or so. So how is yours?
New replacement air filters for the 2 litre cars can be the K&N part number E4530, (it’s a tight fit, but it does fit! – Adrian Berry)
K&N Filters are available from a number of suppliers.
Specifications: 5-7/8″OD, 3-1/8″ID, 3-3/8″H
K&N Small Engine and Light Industrial Replacement Air Filters – K&N manufactures many direct replacement elements
for small industrial engines, utility lawn and garden units, air compressors, generators, chain saws, etc.
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