Club 80-90 Forums

Now before everyone starts I realise a lot of people prefer the original pierburg and this thread is not aimed at saying one is better than the other etc.
Like many others I became the owner of a van that had already had the weber 34 dat conversion fitted and for a while I have been quite happily pottering about in it. While I know a lot of people say they never run right with a weber I have yet to have any major problems.
The only issues if any were a bit of a flat spot before the second barrel opened up and seemed to struggle a little at top end (60-70mph) which I often attributed to the large leisuredrive hardtop.

Following a good service including new leads, plugs, rotor and cap I thought it was time I had a bit more of a read around the progessive carb. While not a huge amount of information is out there relating to the vw there was quite a few sites relating to the 34dat, dmtl or other variations fitted to lancias and fiats. A further dig threw up various interesting threads about getting pregressive webers to work well on air cooled vw.

Mine had the original jets as per supplied kit:
Idle 50 / 80
Main 117 / 165
Air 190 / 145

Following advice from someone at Aircooled.net it was suggested to try an alternative setup as such currently I now have
Idle 50 / 65
Main 125 / 170
Air 160 / 180

Much smoother power delivery, flat spot is eliminated and pulls better up to 65-70mph. I've yet to live with it for a while and see how economy is affected but am hopeful it should be about the same.
Yes a rolling road session would probably be the next step but for home tuning confirmation with plug colour, a gunson colortune and maybe a co meter this will do for now.

ash1293 wrote:Attention happy weber 34dat owners.

That'll include me then

I don't know if you saw my thread at https://club8090.co.uk/forum/viewtopic.p ... p=8223172&.

As I said, I'm not great with carbs and may therefore have mis-identified components, but putting into the same format as you I "might" be running

Main 145 / 165
Air 195 / 117

I hope yours were in better condition than mine.

Does that make sense - happy for you to translate the meaning of the numbers for me ?

937carrera wrote: I don't know if you saw my thread at https://club8090.co.uk/forum/viewtopic.p ... p=8223172&.

As I said, I'm not great with carbs and may therefore have mis-identified components, but putting into the same format as you I "might" be running

Main 145 / 165
Air 195 / 117

I hope yours were in better condition than mine.

Does that make sense - happy for you to translate the meaning of the numbers for me ?

Must have missed that thread.

I'm no expert but here is what I have gleamed so far......

Right - think you may have mixed things up a bit.



Primary and seconday idle jets are in two parts - tight interference fit. Its only the tip you change and retain the top screw.

Primary and secondary mains are in three parts - the tip which is the main fuel jet, emulsion tube (by all accounts changing this is a dark art and best to leave alone) and the top screw it is an air corrector.


Primary idle jet - not just for idle but contributes at low revs before primary kicks in.
Secondary idle jet helps fill the gap as the second barrel starts to open before coming on to secondary main.

Main jets - generally available in steps of 5 - each step up richens across the full range of that barrel.
Air correctors - generally available in steps of 5 - each step up weakens mixture as revs increase towarsd top end. Generally 3 steps here equates to 1 step with main jet.


For example:
Primary main jet as per original kit is made of a 117 jet, f30 emulsion tube and a 190 air corrector.
Secondary main jet as per original kit is made of a 165 jet, f25 emulsion tube and a 145 air corrector.

Primary idle 50
Secondary idle 80

In theory unless at increased altitude primary idle rarely needs to be above 50 - I have a 55 to try if needed but doubt I will.
Secondary has lesser affect and depending on use is sometimes set the same as primary - strange that weber decided for such a large one at 80.

Does that start to make more sense?

Includes me too

Since the engine rebuild (carb had been refurbed recently as well) she’s been running superb and will deffo be going on a rolling road sometime soon. I also think the Speedshop exhaust has assisted positively with running as well.

300CE wrote:Includes me too

Since the engine rebuild (carb had been refurbed recently as well) she’s been running superb and will deffo be going on a rolling road sometime soon.

Would be interesting to see what setup they suggest.

I’ll have a chat with him and I’ll report back once I’ve had it done

Cheers for that, starting to make a bit more sense now. Great picture by the way

So,
Primary emulsion tube and jet ; 117 main jet with 195 air correction
Secondary emulsion tube and main jet ; 165 main jet with 145 air correction

back in your format

Mains 117 / 165
Air correction 195 / 145

almost standard

My engine setup is a bit more complicated as it's a DF case, with DG intake & heads and an unknown cam, probably DF

I'm a lot better with FI, including K-Jet too much dark art that I don't know with carbs. Mind you, I have only really had one carb vehicle before the T25 and the 412LS

ash1293 wrote:
Must have missed that thread.

I'm no expert but here is what I have gleamed so far......

Right - think you may have mixed things up a bit.



Primary and seconday idle jets are in two parts - tight interference fit. Its only the tip you change and retain the top screw.

Primary and secondary mains are in three parts - the tip which is the main fuel jet, emulsion tube (by all accounts changing this is a dark art and best to leave alone) and the top screw it is an air corrector.


Primary idle jet - not just for idle but contributes at low revs before primary kicks in.
Secondary idle jet helps fill the gap as the second barrel starts to open before coming on to secondary main.

Main jets - generally available in steps of 5 - each step up richens across the full range of that barrel.
Air correctors - generally available in steps of 5 - each step up weakens mixture as revs increase towarsd top end. Generally 3 steps here equates to 1 step with main jet.


For example:
Primary main jet as per original kit is made of a 117 jet, f30 emulsion tube and a 190 air corrector.
Secondary main jet as per original kit is made of a 165 jet, f25 emulsion tube and a 145 air corrector.

Primary idle 50
Secondary idle 80

In theory unless at increased altitude primary idle rarely needs to be above 50 - I have a 55 to try if needed but doubt I will.
Secondary has lesser affect and depending on use is sometimes set the same as primary - strange that weber decided for such a large one at 80.

Does that start to make more sense?

Too early to say for certain but so far it makes for a much nicer drive.
Have yet to do any serious miles or at a cruising speed of 60 but on the shorter runs back and forward to work etc its much smoother delivery and doesn't need to be shifted down as much. Nor am I feeling the need for such a heavy foot to make any real progress.

A good explanation of the function of the air correction jet here

https://www.classiczcars.com/forums/top ... explained/

I’ve upped the primary air corrector to 170 and it’s been driving well returning around 22mpg. Considering it’s a kitted out high top it doesn’t seem too bad.

I’ve a few little more tweaks to try and will update in due course.


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Hi all.

Just trying to fit a 34 dat ....

Tho it looks like the superfeed jet in your pics is missing from my unit.

What's the best size for this one. And a good place to get it from might help.

Cheers in advance

Steve

Here's the pics

Might be worth giving these chaps a shout:

https://www.dellorto.co.uk/product-cate ... ors-parts/

Thanks for that. I've emailed them..

Nevertheless , I had it running tonight.

A few teething problems but seemed OK by the end using nuggets from this forum .

Quick couple of questions...

1. The little spring .....it was only attached at one end. On the main throttle lever ball..... any ideas where it goes.
2. There is a short fuel hose ( 1 inch) off of a port tube at back of the carb ( nearest front of vehicle.)
Is this a fuel breather.? Do I need to do anything with it?
3. No where for the vac hose off the air filter box to go.....is this important....?

Ah , and yes, I have fixed the idle shut off , cable had snapped off. Tested it too , seemed OK.