The restoration of carburettors to as new condition can be a major undertaking when carried out correctly. It is therefore important to evaluate if it is viable from a cost perspective, particularly where a new carburettor is still available as in the case of the Weber DCOE series of carburettor. However, where a specific model of DCOE was fitted as original equipment on a vehicle it may well be the correct policy, i.e. Ferrari, Alfa Romeo, Maserati and Lotus to name just a few.

 

Weber carburettors are essentially a precision fuel metering device, they are extremely well designed with reliability that often resists the ravages of time.

Nevertheless, when buying a second hand carburettor(s) a certain amount of caution is required. It can be difficult to assess if it is still as good today as it was when new, because quite likely it could be well over 50 years old.

 

With personal experience gained from over 35years as a fuel system development engineer. During this time, I designed many Weber carburettor kits, to replace most other makes of carburettor used by many motor manufacturers, the majority of which had failed due to inferior design and quality. Therefore, it is very understandable that a significant amount of Weber carburettors still appear for sale on auction sites. These include not only Weber performance carburettors (DCOE etc) but also motor manufacturer O.E. fitment carburettors, and the Weber Direct Replacement kits designed and developed by my department at Weber Concessionaires/Webcon. Having said that it is only to be expected that some deterioration will have taken place over possibly half a century, since they were produced.

Therefore, once again it has to be stressed, that there is likely to be various faults that will need to be rectified, and in some cases, it might mean the carburettor is beyond repair or economically not viable to restore.

The following cautionary information details some, (but certainly not all) of the issues to be aware of -

 

Damage, Corrosion and Seizure

Damage, this includes worn, broken/damaged castings, also internally float assemblies and calibration parts can often be damaged or seized.

Corrosion and seizures due to neglect can be a significant problem.

Internally corrosion can also result in damage to the seating faces for the calibration components, this includes jets and valves . It may be possible to re-cut the jet seats providing the corrosion is not excessive using the correct service tooling. However, if not corrected, this will seriously affect the fuel metering (calibration) of the carburettor, this may ultimately result in damage to an engine.

 

 

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Throttle Shaft Excessive Wear and Seizure

Many Weber carburettors have ball race bearings, these deteriorate with age, use and corrosion. Throttle shafts can also become damaged and distorted (twisted) through misuse, often due to poor throttle linkage design.

Although the bearings can be replaced, it's important that the bushing in the centre journals are not excessively worn. Carburettors manufactured before the 1970s were produced with brass throttle shafts that are very often worn where they pass through the central journals of the carburettor. For this reason, in most cases brass throttle shafts will need to be replaced – see Fig 2.

In the case of the DCOE carburettor, although the replacing of the shaft itself is not a difficult operation (unless seized), the difficulty arises in the critical drilling of the shaft to correctly position the accelerator pump lever. To do this successfully, to ensure the accelerator pump discharge is correct, special service tooling is required, without this a mistake will destroy an expensive throttle shaft.

 

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Damaged Idle Mixture Port

This is a frequent problem with Weber DCOE carburettors, where the idle mixture screws have been over tightened causing the needle to break through the mixture port in the barrel of the carburettor, (located upstream in relation to the throttle plate). - see Fig. 3

This damage will result in very poor engine idle quality due to the correct idle mixture adjustment being unattainable.

N.B. Carburatori are able carry out repairs to recover the damage, should it be considered worthwhile, but additional costs are involved in the repair procedure.

 

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Previous Restoration Damage

The problem can quite commonly be due to previous poor rebuild / renovation work.

Although there are many carburettors for sale on auction sites that look to have been restored and are perhaps excellent in appearance, very few show the internal details and even then, many of the faults described here cannot successfully be identified without examination.

Processes such as soda or vapour blasting and ultrasonic baths can produce good looking castings but they will not clear a fuel gallery that has become blocked with the residue of evaporated fuel and contaminates that can build up particularly in carburettors that have remained unused for many years.

N.B. 1 All blasting processes use a particulate medium to abrade the surface to achieve a desired surface appearance and finish. However, it is extremely important that the carburettor undergoes a further ultrasonic process and washing to ensure all particulate blast medium is completely removed. If this is not carried out thoroughly, it is likely that obstruction will occur within the carburettor, the idle and accelerator pump circuits being the most vulnerable.

N.B. 2 More importantly should any blast medium be drawn into the engine serious damage will be inevitable. Fig. 1 & 4 show a typical example, where a Weber DCN carburettor has undergone a vapour blast process whilst still fully assembled, and it was purchased by myself from an auction site, my mistake!

 

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N.B. 3 The majority of experienced engine builders are aware of this problem, and will not accept carburettor(s) and engine components supplied to them that have undergone a blast process, unless from a reputable and reliable source.

 

Fig. 5 shows a Weber DCN carburettor from a Ferrari 365 GTB that has undergone a poor previous restoration. On this occasion using a damaging erosive blast medium, and as can be seen the throttle plate 78 deg. stamping has been almost removed by an aggressive basting operation. More importantly this kind of blasting destroys the bore of the carburettor in the location of the throttle plate seriously affecting the slow running idle and progression quality of the engine. Difficulty in achieving a balanced air flow through each carburettor barrel is to be expected. A well-known Ferrari Specialist brought the six 40 DCN carburettors for corrective work following the previous poor restoration. Although damaged by the blasting process, we were able to recover the carburettors to an acceptable state, thus saving the customer many thousands of pounds should they have needed to be replaced.

 

Finally, without the experience, equipment and tooling that is required, it will be extremely difficult to identify and successfully rectify many of the faults detailed here. Furthermore, this is not an exhaustive catalogue of all the possible faults that need to be considered when buying second hand Weber carburettors, it is only an example of some of the more common issues – Caveat Emptor!!

 

When purchasing carburettors or restoration work from Carburatori, you can be confident that they have been restored to the highest standard using the original correctly manufactured parts supplied by Webcon or from Carburatori's own stock which is either Weber in origin or reproduced to the correct specification by ourselves. We also have service tooling, test equipment and the technical data necessary to ensure the carburettors are within the correct factory tolerances and specification.

 

With all our sales, we offer technical support to ensure the customer is satisfied with any purchase, this includes initial assistance with regards to fitment and calibration advice along with any relevant technical data and information.