Twin Sidedrought Webbers

[Thotos]

A while back when I was at Omicron  I saw a 2 litre twin cam engine being prepared for a racing Lancia Montecarlo. I noticed that the twin sidedrought carburettors were mounted on the manifold with spring washers under nylock mounting nuts which were not done up very tight.  When I commented on this, I was told "you NEVER fully tighten these carbs as you'll get fuel frothing from the vibration". I was told that the carburettors should either be mounted using spring washers or by fitting large rubber washers under the nuts. The idea apparently is to stop the transmission of some of the engine vibrations to the carburettors. The carburettors on my engine are solidly mounted and I don't know if I should be changing this as the car runs fine (most of the time!). Does anyone out there know more about this?

[djape1977]

first time i ever heard of something like this. a friend of mine is a racing driver who prepares his cars himself for 20yrs (most are fiat or fiat based), and i newer saw anything like that on any of his cars. carbs are always mounted the usual way.
in my opinion, what you were told is a big BS. i don't see how one could decrease vibrations of carb that way even if it did make diference

[mirafioriman]

I have always fitted sidedraught carbs in the manner Theo has described above. In the old days it was 'Thackray' washers (like a small coil spring) nowadays you get little rubbers which have cupwashers either side. The correct method is to use feeler gauges to set the small gap to get the correct tension.

[sid131]

Dave please enlighten me on that one?

[mirafioriman]

I think I spelt 'thackray' wrong, see the FMC site!

I can not remember the gap off the top of my head, but basically the idea is that the feeler gauge allows you to put the carbs under the correct tension so they are tight enough to not draw air, but not too tight that vibration becomes a problem.

[Thotos]

Thanks for the input Dave. I've looked up "Thackery washers". See http://cgi.ebay.co.uk/WEBER-CARB-SET-OF-16-THACKERY-WASHERS-5-16_W0QQitemZ350188733561QQcmdZViewItemQQptZUK_CarsParts_Vehicles_CarParts_SM?hash=item350188733561 on ebay. The rubber washers and cups seems like a neater way to me so I'll probably go for a set of those (see photo below).

 

[mirafioriman]

The rubber washers are better in my opinion as they do not fatigue in the same way as the Thackery washers can.

[djape1977]

when you do fit those please report the results.
still, i don't see how that could make any diference 

[Thotos]

As I've said the car runs fine  so I don't know what improvement, if any, I should expect. But I've just ordered a set of 8 MISAB rubber washers with 16 matching metal cups from ebay (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=110328253888&ssPageName=ADME:B:EOIBSA:UK:11). I already have a new set of gaskets (or MISAB mounting plates as they call them  ) so I shall add this work to my list of things to do in getting ready for 3ma09.  I'll let you know if there's any noticeable improvement in anything.

[parrish]

Theo,
the misab washers you refer to are infacts misab 'O' rings and are the manifold to carb connections, you dont need 8 only 4, these 'O' ring's assisit with the anti foaming only if used with the correct rubber or spring mounting of the carbs, most performance shops sell the lot as a kit. Remember when fitting not to tighten too much, your only trying to makwe them air tight, the nyloc's will keep the carbs on the manifold.
Steve.

[djape1977]

what about ordinary single downdrought setup then? no foaming there?

[alan.acs]

I have been working on rally cars for over 20 years and have never seen side-draughts mounted with out a version of the misab or cosworth mounts.they also help reduce the heat transfer to the carbs and the fuel.
 You should not fit side draughts with out these.

steve c .   Information is spot on as always.

[jasonh131]

Heres a reply from martin S.F.C.

This method of mounting has been around since the seventies.

I first used this type of spring washer on a Mk1 Escort twin cam rally car with Webers. The use of spring or thick nylon washers tends to change the main damping frequency - but the spring washers worked ok in & with the Escort. If the setup is exposed to more race 'g' then you may need more springing

This was not the main problem, as the Ford agent supplied fitting kit had 'O' rings to mount the carbs, and they leaked when the car got up to some rally antics and the larger spring set up is meant to stop the 'O' rings leaking (new noise regulations had come in and the intake was ducted into the cabin for a bit - and you could hear the leak hiss).
So Misab Plates were quickly used - and they come with their own form of spring washers - again must not be over-tightened for the same reason. You should always try and use oversize Misab plates, so with 40mm carbs use 45mm Misab plates, with 45mm carbs use 48mm Misab plates etc. as they last a lot longer if kept out of the main airflow. Usually they were supplied with Thackray washers, and they last longer than the cup washers - but are more expensive.

I've seen both general frothing and specific frequency frothing, and it will seriously upset the carbs - you'll know if you're suffering from it.
The Weber manuals will give you the set up details (I can't remember them now - years since I had side draughts).

Southern Carburettors have/had a pamphlet and are a recommended SFC supplier.
This post will be moved into the Troubleshooting forum in a few days
Martin

[sid131]

i have the problem of the carbs going out of balance on the celica, asain twin carb set up every now & again they are fitted with 2 ramflo filters i also have the same filters for my 131 & i use the carb balancer for the formula v (irish champion Brian Hearty lives nearby) he loaned me his at first & then i bought my own & got adaptor for the toyota made up from nylon so fiatfactory is correct about the carbs going out of balance with twin filters, my honda cb900 has 4 air filters & i have morgan tune kit to tune it  used to do that every couple of weeks or so, bike hasnt even been started in 4 years now!
finally these carbs are ment for performance & if you dont drive the wire outa the car they will play up so theo give her plenty she sounds lovely on the youtube vids, if i was you i would leave well alone.

[Aussie131]

At most this is all you need to run, we have run webers in every format u could imagine, being rhd we can run side drought webers on a standard 131, 124 cause there is no master cylinder in the way YEA!!!
just thought id have a brag

http://cgi.ebay.com.au/SOFT-MOUNT-KIT-WEBER-45-48-DCOE-DELLORTO-DHLA-SOLEX-PHH_W0QQitemZ330327786750QQcmdZViewItemQQptZAU_Car_Parts_Accessories?hash=item330327786750&_trksid=p3286.c0.m14&_trkparms=66%3A2|65%3A1|39%3A1|240%3A1318|301%3A0|293%3A1|294%3A50