Carbs Rebuild

[Garfield]

Any recommendations for a set of Webers...

Everyone has mentioned Southern Carbs in Crawley. Unfortunately they have a three month waiting list ....

Thank you.

G

[911hillclimber]

Canford Classics must be top of the list?

Nick Moss too I suspect.

[Lightweight_911]

Chris Flavell at Fenn Lane Motorsport ...

[jamie]

Gower & Lee did a lovely job of the DCOE40 on my Renault.

[mycar]

How about having a go yourself ? These sites are full of information.

https://s-media-cache-ak0.pinimg.com/73 ... 885197.jpg

http://www.performanceoriented.com/

If nothing else they'll prepare you for any discussion about secondary venturis and idle mixture adjustment screws you might find yourself having.

[Nick Moss]

Any recommendations for a set of Webers...

Everyone has mentioned Southern Carbs in Crawley. Unfortunately they have a three month waiting list ....

Thank you.

G

Southern Carbs do all mine.

[neilbardsley]

http://www.webcon.co.uk/ for new and maybe they do rebuild?

Chris Turner uses them. I think they are almost on his way home. http://www.christurner.com/

That said what needs doing? As with the correct kit Chris or another on here can do the rebuild for you? If you call him I'm sure he will be able to help.

[911hillclimber]

I tried Southern Car some years back, great people but not all parts are available, and my webers then were not complete.

Rebuild can be a clean and new gaskets, but isf the spindle bores are worn then it gets far more involved.

Gary and Hassad on here are good references for the tougher route.

My rebuild kit came with Teflon sleeves to take the normal wear out of the body/spindles so giving a significant reduction in excess air passage to the intakes.

imho this area is crucial to the success of the job.

As an aside, the PMO 'webers' from the USA use sealed precision ball races for these bearing points and use the commonly available DCOE jets that everyone sells and has at rolling roads. Tripple choke carbs can spook some RR tuners, even veteran ones like I've used.

This is a DIY job unless you are faced with large body wear.
Hassad might do them for you as he is offering engineering services now.

[fetuhoe]

The PTFE Supports (Item 78) are only used on the outer two 'bearing journals' so if wear has occurred on any of the other 4 journals then you will still have issues.

The outer journals are also a larger diameter so that you must fit these parts or the potential air leak will always be an issue.

The very early IDA 3C and 3C/1 didn't have these supports and had a bronze bush.

Weber used to supply an 8.5mm diameter shaft to resolve the problem of wear on the early carbs and this really means you need a parallel reamer about 220mm long so you can ream two of the bores together.

On the later carbs with the PTFE supports are already larger diameter than 8.5mm so even if you fit an 8.5mm diameter shaft you will need to open up the end bores and make a slightly longer PTFE support strip to replace this part.

Wear in the bore is also quite common and this can prevent the throttle plate from seating correctly and it is not bad practice to hone the bores to about 0.25mm over size and fit new throttle plates to suit this diameter and to be certain that they seal correctly.

Depending on the application there are a few other mods that can be helpful to the behaviour of these carbs.

For example if you are fitting Webers onto a modified engine or an engine of a different capacity to the original engine it is quite common to experience slight hesitations or flat spots at certain engine revs.

This is commonly associated with the behaviour of the idle jet and its associated air corrector.

These parts of the circuit can impact on behaviour up to 3000rpm and need tuning to suit specific applications.

It is obviously simple to change the idle jet but the Air Corrector for this jet is a simple bush pressed into the body of the carb and in general it cannot be changed.

It is this part of the progression circuit that commonly helps to create stumbles.

It is possible to modify this part of the carb and install a 'tuneable' Air Corrector which does help.

The PMO is equipped with tuneable idle jet air correctors as standard.




There are also some anti-percolation mods which improve hot starting which is another potential problem.

Here are some Zenith 40TIN carbs we overhauled last month.

[Project 911]

I'm doing mine now and having brand new large ultrasonic cleaner, any suggestion what should be removed (so not washed in cleaner) from carbs before giving them ultrasonic clean? (I'll fit rebuild kit after cleaning)

I will need to search some info how to measure shaft wear... Fingers crossed they will be ok.

[haasad]

Total strip including all gallery plugs , don't rely wholly on the ultrasonic cleaner its essential to verify all ways are clear and clean with carefull use of soft probes and air lines. Be prepared to clean the parts a few times.
The shafts are a nominal 8 mm diameter.
Check the butterflys carefully to, excessive wear or edge steps will cause idle issues. Plain 48 deg butterflys for 40 DCOE's fit fine and are widley available, don't use the ones relieved for transition.
You will likely need new butterfly screws too again these are widely available but check head type thread and length. Some folks use loctite to retain these with good results but being fussy I used loctite and staked mine .
If the shafts are ok but the bores are worn it is possible to have them line bored and to fit new bushes, Paul Abbot at Performance Oriented suggested to me that doing only the outer bores was a viable proposition and easier if you don't have much wear since it takes up the "slack" and air leakage via the others remains contant as the shaft is held thus the mixture can be set accurately.

[Gary71]

I replaced just the outer on my Zeniths with a sealed roller bearing and it massively improved the idle and low speed running.

I only sealed the end bearing by the throttle quadrant as it is the only one that showed any movement. The other reason is the bearing seals inevitably add some sticktion to the shafts and I didn't want to introduce more problems than I solved. I tested the idea on an old set first before committing!



I removed the bushes from my old spares bin set of Zeniths and a friend machined them down to suit the size of the new roller bearing.



I wanted to maintain the machined surface inside the throat so the tricky bit was putting them back in lined up to get one surface again! After a couple of goes it was sorted.

I used a bearing sealant on the outer surface to hold it in place then pulled the roller bearing with a bolt.

[Project 911]

Excellent, many thanks!!

[fetuhoe]

Gary,

Do you think that the shaft is hard enough to run against a needle roller without brinelling?

The general recommendation for a lightly loaded shaft would 58 HRC with a surface finish (Ra) of better the 0.2 microns.

You may see fairly rapid wear of the shaft as the rollers may fret the surface of the shaft particularly in the absence of any lubrication and this does happen even with very low loads.

I would be interested to know more about the seal, which is designed to be compatible with grease and how it will react to Ethanol ?

[Gary71]

I have no idea! Before this the shafts wobbled and breathed more air than the idle circuit, after they didn't and the car has run sweet for many thousands of miles. I'll worry about shaft wear on the already worn shafts at a later date

The seals are nitrile, so yes they are resistant. I also greased the bearing before final install. That will disappear in time I'm sure but let's be honest it's not spinning at 10000 rpm is it