Car Carburettors

Weber IDA3 series carburetors

Car carburettors: Weber IDA3 Comprehensive overhaul (Picasa Gallery - opens in new window)

Comprehensive Overhaul:

A similar method to that described for the 2 barrel carburetors above is used. However, if this work is done correctly it is a very time consuming process.  There are other matters of concern: 

•Replacement carburetors are difficult to source.  New ones are unobtainable and the modern equivalent, built by the US company PMO are extremely expensive.

•The spares situation for IDA3’s is equally grim.  Great emphasis needs to be placed on conserving these instruments.  This applies particularly at service or overhaul time.

•Rebuild kits are available.  In poor quality kits essential components are missing.  These have to be sourced if overhaul work is to be completed properly.

•These instruments are now 30+ years old and will have “enjoyed” the attention of many hands in their earlier lives.  Experience indicates that carburettor maintenance standards vary from the very good to the abysmal, with a depressing number at the lower end.

•THE issue that should cause you more concern than any other is the potential for wear in the throttle shaft bearing surfaces.  Play of this sort will allow air to be drawn in past the bearing surface (mainly at idle) and thus prevent accurate tuning of the carburettors.  More importantly if play in this area is left unchecked it will eventually ruin the carburetors.  As soon as play is detected, remedial work should be considered.  Look very carefully for throttle shaft bearing surface play. It is often more easily heard than felt, particularly if the carburetor is dirty. Wear tends to take place in the direction of airflow, thus at right angles to the throttle shaft axis.

JRS offer a comprehensive repair service but ONLY when carburetors are undergoing a Comprehensive overhaul or Restoration.  Remedies will depend on whether the bodies are early (brass bushed bearings) or later (PTFE bearings) and the condition of both long and short throttle shafts.  The usual remedy is line boring and rebushing carburetor bodies, but the JRS preferred option (and the original Weber solution to the problem of shaft bearing wear) is the provision and installation of oversized throttle spindles.

Why?

Although not usually understood, typically rebushing repairs are restricted to the outer bearing surfaces yet wear in these surfaces must translate to wear in the inner bearing surfaces. Rebushing will not resolve this problem.  However, the provision of reamed 8.5mm bushes in both outer bearing surfaces, together with the oversize reaming of the inner bearing surfaces and the fitting of oversized throttle spindles will provide you with a well engineered and comprehensive solution for throttle shaft wear.  That is why Weber manufactured oversize shafts.  This is why JRS also manufacture oversize shafts.

There are other areas in these instruments that need careful attention. Pump housings are an example. Again, Weber state the float height in accuracy terms of + or – 0.50mm. This degree of accuracy is virtually impossible without taking play out of the system.  Float heights need to be accurate across both chambers on an instrument and across all instruments on any particular engine. This piece of work is extremely difficult to do with the carburettors on the engine – evidence suggest that many people try!! There is little point in spending time synchronizing air flow if fuel levels are different.

In common with all Weber carburetors of the sort dealt with at JRS, the manufacturer carefully sizes all internal components but if jet seats etc are damaged, fuel control is compromised  – jet seat condition is important.

All of the above are considered by JRS in the process of overhauling  /cleaning and rebuilding a set of these instruments.  The appropriate tooling is available and work is completed to the usual high standards.

Costs (IDA3C)

Comprehensive overhaul: including full manufacturer’s rebuild kit and return carriage:        £225 per instrument 

Throttle shaft repairs: Costed on an individual basis. (The type of repair will depend on the condition of the shafts.)  As an example, in a case where the wear is in its earliest stages and the throttle shafts are undamaged and wear to the inner bearing surfaces is minimal,  line boring and rebushing the outer body bearing surfaces in brass would be an additional £50 per instrument.

Oversized throttle spindles:  Where throttle spindle wear is a problem, JRS can install both long and short spindles available in 8.50mm oversize.  These are only available on part exchange of complete original shafts. Prices on application.

********Shafts are NOT available for retail sale.**********

COST COMPARISON

A SINGLE new PMO 40mm carburetor costs $1450 (£725) in the US, so carriage, UK Customs duties, VAT etc to pay in addition when imported into the UK.  If you want the full PMO kit as well it is $1750 (£875) per carburetor again plus carriage, Customs duties, VAT etc.

If you have a sound pair of Weber IDA3C’s, JRS can comprehensively overhaul them and rebush and refit the original throttle shafts for less than the cost of a single PMO. 

Restoration:

A restoration service is also available.  Details on request.

If you wish to use this service, or would like to know more about any aspect, then contact Mike Davies at JRS on (UK) 01792 402458 or email Mike on: jrs@jrs.uk.com

JRS/UCC offer an engineering approach to carburettor overhaul, cleaning and restoration: Attention to detail, high quality workmanship, years of experience and the use of modern machine shop facilites and ultrasonic cleaning equipment produce excellent results.

General Information

All Weber/Dellorto overhaul, cleaning and restoration services are not to the same standard or the same cost.  Compare like with like – quality then cost.

This website states clearly the costs, the processes used and the extent of the work completed by JRS.

Years of experience are available to you.  The only car carburetors worked on here are these Weber and Dellorto instruments.

If your carburettors need work, consider getting a couple of quotations before deciding on where to place the work. Compare the service quality and then the cost.  Cheap and cheerful is not the place to send your carburettors – you need to be sure about who will complete the work and to what standard. JRS standards are clearly stated in these pages – this standard is applied to every piece of work. A job bodged could be a set of carburetors ruined!! As far as costs are concerned, try and ensure you are comparing like with like. Is VAT payable?

Ultrasonics is the most effective cleaning process currently available. The JRS equipment, complemented by the effective cleaning solutions, temperatures, working practices and experience will greatly improve the performance of your carburettors and thus, the performance of your engine. Nothing, however, will remove wear. Happily in these instruments there is little to wear and what does (over long periods) is replaceable.

The quickest and cheapest method of carburetor cleaning is acid/chemical dipping. Acids work by eating into spoils and metal. The high points in any metal are attacked first and in the case of your carburettors, that includes all unprotected threads. There are problems enough with the fine threads in these carburettors without increasing them by the use of acid based cleaning. Ask for a specification before placing the work or assume that acids will be used. Acids and aggressive chemicals –quick, cheap and potentially harmful and as far as appearance goes, make your own comparisons –the JRS Gallery is full of pics of work completed here.

Whilst the physical condition of the carburetor components is important, THE ACCURACY OF THE BUILD IS CRITICAL. Over the years many hands will have worked on your carburetors and experience at JRS indicates that much of this work will have been poorly done.

Whoever you use, UNDERSTAND THE DIFFERENCE BETWEEN CLEANING AND OVERHAUL.  Then help yourself:  Spare parts are expensive so take a little time to ensure that you will need as few as possible

•When you get your instrument back from cleaning or overhaul and before  final tuning, take out as many of the external  threaded components as possible (one by one), coat the threads with anti seize paste (Copperslip) or similar and replace them. You may find that some fittings are seized and you should ask your supplier/overhaul person to remedy the problem. None of the threaded components should be locked in place:- all should be removable. Lastly remove the main spindle spring and test the bearings whilst not under load. If gritty or stiff then get your supplier/ overhauler to remedy the situation- perhaps there are still chemicals in there!!.

•The idle mixture screw is set in a tower which happily collects debris and moisture which can make the adjustment/removal of the screw difficult. Either pack the top with grease or put a silicon cap on it.

•The threaded rod that operates the pump can snap under the adjusting nuts. Replacements are difficult so ensure that you do what you can to reduce the chance of this happening. This can be achieved by greasing the rod and using two spanners of the correct size when required.

Happily, you will not need to complete any of the above if your cleaning or restoration work has been completed by JRS.

It has already been done.

Customers from outside the EEC should contact JRS for the appropriate UK customs information.

Tel: 01792 402458
E-mail: jrs@jrs.uk.com