Correct carb?

[itchyfeet]

Fit a lambda sensor and air fuel guage and by all means tune it yourself from driving experience, it's what you would do with lpg, the guage just gives you confidence it's not running overly lean or rich.
fitted my cheapo one for about 60 quid iirc

[CJH]

...the guage just gives you confidence it's not running overly lean or rich.

That sounds like exactly what I need, thank you. I'll look into that.

[MGP]

The information on the carbs that you have listed suggest that the dg is struggling to breathe through that carb or that vw has set it to run on the lean side.
With the extra displacement and the increase in ve that the improved cam will give I would make an educated guess that you will be moving enough air to make the weber dmtl work well.
Also with the dmtl there is a huge range of fuel jets, emulsion tubes and air correction jets
By all means set the carb up yourself as said you only need an afr guage, a wide band would make life easier as you would be able to see how far out you are as opposed to just rich or lean.

[CJH]

Thank you again. So what is it that suggests it's struggling to breathe? I guess I should also post the jet sizes for the corresponding secondary venturis to get a fuller picture. If it's the primary venturi size that's an issue, maybe there's a case for using the slightly bigger LT carb body? I guess I'd have to open out the corresponding hole in the manifold.

I can appreciate that the fuel/air mix has to be right, and that benefiting from more fuel is dependent on it also moving more air. To that end I should perhaps mention that I'll be fitting a Speedshop stainless exhaust to the 2.1 - no idea how much bearing that has. Not much I reckon, given that it's the air in the combustion phase that's important.

The air filter is the standard '83 version, and in fact I'm keen to keep it all looking original, so I don't see me changing to a different make of carb. This whole exercise is really just about looking for ways to make better use of what's there. Maybe there's a better breathing air filter that fits the square housing?

By the way, what's 'ev'?

[itchyfeet]

...the guage just gives you confidence it's not running overly lean or rich.

That sounds like exactly what I need, thank you. I'll look into that.

don't buy that exact guage I have it's cheap but annoying with a smoked face which I removed and colour change backlight, will be replacing this one.

20 quid bosch sensor
http://www.ebay.co.uk/itm/UNIVERSAL-LAM ... 3cef0bcecb" onclick="window.open(this.href);return false;

3 quid weld in boss ( stainless also available)
http://www.ebay.co.uk/itm/Lambda-boss-N ... 3a83b0e1ca" onclick="window.open(this.href);return false;

cheapo gauage £16
http://www.ebay.co.uk/itm/S2-52mm-Air-F ... 27f2072788" onclick="window.open(this.href);return false;

pod £10
http://www.ebay.co.uk/itm/Tim-52mm-Oil- ... 3f47860f21" onclick="window.open(this.href);return false;

[CJH]

Excellent - thank you! I believe the Speedshop exhaust already has a lambda sensor boss. Surely that's another sign....

[MGP]

Ve is volumetric efficiency and it is how much air you engine moves with each stroke.
Ve is expressed as a % so 100%would mean that the cylinder would completely empty itself of exhaust gasses and fill itself with fresh air and fuel.
In reality a 2v per cylinder road engine will probably only manage about 75 to 80% at best.
Looking at the small jets in the dg carb would sugest that the air speed and vacum on the jets is high meaning the carb is a big restriction possibly to get better fuel atomisation because of the long inlet tract after the carb and the tendancy for the fuel to fall out of suspension.
Look at the engine as an air pump and forget combustion for the moment, you want it to to be as efficient as possible and to work at the best of its ability? Then you need to allow the air going in and the air coming out the easiest path posible.
I think thet the lt carb would still be a compromise as the increase in venturi size is proportional to displacement increase however if you fit the cam you will be opening the valves for longer increasing the potential ve but strangling the enging with a small venturi.
The lt carb will be better than the dg one however you may find that it will require smaller jets. A good place to start would probably be the jets from your dg carb with possibly a smaller air correction jet.

[silverbullet]

Also the DG was the last iteration of VW's 69mm crank which was always a bit in the short side, so piston acceleration was kind of low and that doesnt help when trying to fill a cylinder (also stresses on the reciprocating masses were kept low which was good for reliability at the ever-conservative Volkswagenwerk)
The rod/stroke ratio is just about 2:1 which makes for exceptional smoothness but limits piston acceleration...
A short stroke engine will always be better at higher rpm but thats no good for mpg. VW did a pretty good job in getting that 78PS and 140Nm@2800 but it still runs out if breath at 4800 iirc meaning that it can't make meaningful torque at higher rpm i.e. its deliberately strangled.
The dismal pre-war 5/50 inlet cam timing is also another way that VW tried to wring all the Nm they could ot of it, without throwing mixture down the exhaust.
The DG might respond quite well to a pair of modest sized downdraght carbs but for all the work and cost, efi or full ems and a 2.1 makes a lot more sense in 2015...

[kevtherev]

Look at the engine as an air pump and forget combustion for the moment, you want it to to be as efficient as possible and to work at the best of its ability? Then you need to allow the air going in and the air coming out the easiest path possible.

Delorto DRLA carbs coupled with type 3 inlet manifolds dispense with inlet restriction.
I have driven a 2.1 with Dellorto 36's fitted. I was remarkable!
But like all things power inducing, Dells are not kind to the wallet or to the MPG.
However I have read here that some Dell DRLA 28's were as efficient as the Pierburg, and still offered a daft grin on full chat.

As you point out MGP it's a balancing act that is ultimately won by your needs and the vans remit.

[kevtherev]

The DG might respond quite well to a pair of modest sized downdraght carbs but for all the work and cost, efi or full ems and a 2.1 makes a lot more sense in 2015...

totally agree

[CJH]

The lt carb will be better than the dg one however you may find that it will require smaller jets. A good place to start would probably be the jets from your dg carb with possibly a smaller air correction jet.

Thanks MGP - very informative. Can you explain what the air correction jet does? As far as I can tell from the Haynes diagrams it doesn't appear to be screwed in like the main jets and the idle jet, so I'm not sure if it's possible to swap them over. I suspect as a starting point I'll just put the DG carb on, maybe add an AFR gauge, and get a feel for how it performs with the 2.1. If an LT carb pops up on ebay I might then do as you say. If not, I might just try some bigger jets in a DG carb as a quick test.

The DG might respond quite well to a pair of modest sized downdraght carbs but for all the work and cost, efi or full ems and a 2.1 makes a lot more sense in 2015...

Ian - you're not listening! I'm talking about a 2.1DJ. I'm not setting out to make a vast change - I'm happy with my current 1.9DG - but I figured if I'm going to invest in a rebuild it should be a 2.1DJ. Others on here have used the original DG carb on a DJ with good results, and have commented on the improvement over the DG. But I've not read about anyone trying to improve the Pierburg to suit the DJ, and they haven't had the advantage of your new cam. I think if it turns out that there isn't much I can do to improve the Pierburg then I'll just 'settle' for the gains that the bigger capacity gives me. I'm just trying to understand the parameters that might make a difference.

[CJH]

But like all things power inducing, Dells are not kind to the wallet or to the MPG.

Yes - good point. I don't want to go mad. 23mpg isn't a good point to work down from.

[CJH]

Ian - you're not listening!

I forgot the smiley. No offence meant

[silverbullet]

No sweat. I was just rambling on and fleshing out the conversation, trying to qualify a few statements with some sort of reasoning

[CJH]

That's a relief - I should really wait till you've sold me a cam (or at least agreed a price) before I start insulting you.