carbs

Post by **ermie571** » 25 Nov 2006, 06:38

Hi folks,

while surfing e-bay on the lookout for "bits" for the van, came across some carbs. Trouble is, I don't know what the technical bits mean, and I cannot find any reference to them in wiki?

I have a 2lt cu twin carbs....

They are solex.
They are PDSIT not PICT (though what that stands for I don't know)

I have learnt from the web, Haynes and an e-bay seller that the one on the left is a solex 34 - pdsit 2, and the one on the right is a 34 pdsit 3.

what does the 34 refer to?

One set on e-bay seems exactly right and meets this spec. The other set refers to 26-40 pdsit carb set. What needs to be done to make it work with the van?

sorry for all the questions - maybe the answers could go on wiki?

thanks in advance

Emma

(trying to learn about this van of mine)

Post by **cumbriankeith** » 25 Nov 2006, 10:57

PDSITs in various versions were fitted to various VWs for ages with the Aircooled T3 2 litre being among if not the last. The version fitted to our buses and a few others is unusual in that for idling engine speeds there is a separate and simple carb mechanism. It is integrated into the left carb but supplies fuel/air mixture to both banks of cylinders via a few bits of simple plumbing (but these joints, as well as the pipework that takes vacuum for the brake servo, are prone to air leaks largely thro aging of the rubber fittings).

Once the throttle is opened other parts of these wonderful, complex devices come into play and deliver measured, copious amounts of fuel/air into the engine. Another factor with these carbs/engines is that they are designed to work with a dual vacuum distributor. The carbs and ignition systems are closely interdependent - it only takes one factor to wear/go out of adjustment and it can affect other parts.

The carbs I think you are presently looking at on eBay are PDSITs, but as you have realised one set is wrong for our engines and cannot be modified to suit - there's no idling circuit. The other selection could well be a good buy at the right price but condition and parts missing are critical. If the throttle spindles are worn they need rebushing to avoid airleaks=more cost. The listing does not show if chokes are present, let alone whether they work or not. Some parts are certainly missing from some of the carbs (eg one anti run-on solenoid) but as the guy says it may be possible to get one good set from them. The associated pipes and linkage are nice to have but don't really wear out so would be easier to get hold of - yours are probably just fine anyway.
The manifolds are too long for our T3s - so I guess they are from a late Bay - more room above the engine. If yours are good I wouldn't bother to pay for the cost of posting them.

A couple of years ago I got a pair off ebay which are in fair condition - just about useable as a spare for when/if I ever need mine rebushing. I paid about £30 or so, but the fuel cutoff solenoid was missing - still work tho.

Hope that helps...

Post by **ermie571** » 25 Nov 2006, 11:02

Keith,
that most certainly does, thankyou!

Will keep an eye on that set, then.

Yep, my manifolds are fine, as is all the linkage!

Will print that out and store in the info about van section of the filing cabinet!

Cheers
Emma

Post by **HarryMann** » 25 Nov 2006, 13:36

what does the 34 refer to?

The suffix numbers very often refer to the choke bore size in mm.

Whilst a 40 has 17.6% larger bore diameter than a 34, its area is 38.4% larger - quite a big difference. The numbers may well be 'nominal' rather than exact - a way of coding up the various sizes for airflow. Some carbs have venturi choke inserts that can be changed, retaining the same main carb body.

Going to a larger bore/choke area increases the theoretical power if the engine can cope with it (has been tuned in other ways too, or increased in capacity) but otherwise nearly always results in poor pickup, transition and smooth progression, and would have to be jetted correctly as well.

NB. 'Choke area' is not to do with the 'choke' (cold enrichening device), its a term that's used to describe the smallest part of the main venturi - where the vacuum is greatest and where fuel is normally metered into the carburrettor's airflow, either through a needle/jet or a spraybar at that point. Constant vacuum carbs like SU's /Stromberg etc. have variable chokes as airflow demand increases, and are sized by their maximum choke size.

Post by **cumbriankeith** » 25 Nov 2006, 13:54

I'm not sure what the 34 refers to but it isn't the venturi size, which is 26mm on stock carbs ('26' is cast into the venturi). When Laurie Pettitt rebuilt my engine he said it could benefit from slightly larger venturis eg 28mm ones but I haven't managed to find any this side of the Atlantic. This site suggests I could get some from them but I haven't got round to it yet...

Post by **HarryMann** » 25 Nov 2006, 14:01

But is a 40 larger than a 34?
.. and as I suggested, could it be a comparative 'size' coding of some sort, rather than simply the actual choke size.

Most carbs do (of necessity) need a comparative choke size reference, as this controls their max airflow - the main parameter use to specify a carburretor for a given application.

So what is happening here is almost certainly a '40' is a larger 'body' of the same type as a '34' allowing a larger set of chokes to be fitted, so there would be slight crossover between a 34 with its largest choke sleeve, and a 40 with its smallest.

Pretty sure this is the situation with the DCOE sidedraught Webbers, the 40 and 45 DCOE range.

The classic old 28/36 DCD progressive twin choke Webbers do have nominally a 26mm first-choke and a 36mm second, the latter having much cruder jetting, as it plays no part in idle or low speed pickup carburrettion.

Sorry Emma, too much detail, I'm sure

Post by **HarryMann** » 25 Nov 2006, 14:16

I think this answers it Keith, from your linked site..

The Solex Master Rebuild Kit includes everything you need to rebuild a Dual Solex 34mm Carb, including float and accelerator pump diaphram. This Rebuild kit is designed for use on Dual Solex 34mm Carbs.

The main bore but not the choke is probably 34mm or it can take a maximum 34mm choke sleeve?

Post by **cumbriankeith** » 25 Nov 2006, 17:02

Yep - that would have been my best guess if forced to make a choice.

Post by **ermie571** » 25 Nov 2006, 18:08

Name.....CumbrainKeith/Harrymann Kombo

Subject......solex carbs and the numbering thereof!!

It amazes me how much you lot know

Emma

Post by **cumbriankeith** » 25 Nov 2006, 22:26

Hmm - cumbrain - I might like that more than Cumbrian - I'm not really from Cumbria anyway - just lived here for 20 odd years...

Post by **cumbriankeith** » 26 Nov 2006, 18:48

Hey Emma
Sounds like there's some good ones up for grabs on JK - were off a 1700 but the jetting may be pretty close and changeable if needed - condition is more important - as is price I suppose...

Post by **ermie571** » 27 Nov 2006, 08:32

CumbrianKeith,

thanks,
will go look.....

don't use the JK site so hadn't spotted them!

How will I know if the jetting is wrong?

(I have a feeling I may not have wanted to ask that question...cue Harrymann and Cumbrainkeith discussion....)

Emma

Post by **HarryMann** » 27 Nov 2006, 10:45

How will I know if the jetting is wrong?

It'll go phutt, bang, phutt, phutt, bang...

Should be a fairly simple job to take them out of one and put them in the other, usually quality good fitting screwdriver is all that's needed and a bit of care about dirt, bits of swarf and cleanliness.

Post by **ermie571** » 27 Nov 2006, 13:51

phutt, bang, phutt, phutt, bang

as opposed to????

Assume the bang is the bad bit.....

Seriously though, does the bang refer to backfire? Will it be noticeably underpowered?

Have registered on the JK forum, so will pm the chap when I get back to the home e-mail tonite to confirm the registration.

Thanks for the help

Emma

Club 80-90 Forums

carbs - one for the wiki...

carbs - one for the wiki...

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carbs

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