Jetting on standard DATR/DAT type Carb

[capriblu]

My Car (2000 Coupe) generally runs very smoothly but I have struggled to get idle quite as smooth and stable as I always remember being to achieve with these cars many years ago.  I have a couple of different DAT /DATR 250 variant carbs that I have tried and all are similar.  I'm confident that ignition timing, no air leaks, spark etc. is all good and I'm starting to wonder whether changes in fuel quality over the years have started to make the original jetting a bit marginal?

Has anybody got any experience or thougts on this?

I'm tempted to try some slightly larger size idle jets.  

Presume both the primary and secondary idle jets will affect tickover (as well as low/medium speed and load running)?

What are the standard jet sizes?

I notice in the Haynes Manual (never a great thing to rely on!) that different main air correction jets on the secondary are shown for DATR variants with 1.50/2.10 and 1.5/2.40 (main/air corrector) the former for 1600 and the latter for some 2000 cars.  This seems quite a difference?

Also quotes a 1.00 mm idling jet on secondary for earlier DMTR (1600/1800) v 0.8 on the DATR both for the same 0.70mm air jet size?

Any sage advice welcome ..........  

[peteracs]

Hi

Out of interest, what petrol are you using?

To rule out the ethanol influence you could try the Esso 99 which according to them has no ethanol in it.

Also a few experiences with dirty idle jets needing a good clean.

Also any chance the float is not floating as it used to?

There was also on the LMC forum an older carb where the end of the idle metering needle had become deformed and needed to be reformed.

Just my 2 penny worth...

Peter

[capriblu]

Thanks Peter,

Issue is very minor really but I know all fuel is very different now.  Ive also read that the Esso 99 is ethanol free so i may try that. I generally use Shell Optimax.

I think the settings originally were never super generous in the lower speed / load range.  The jets are clean and the mixture needle is good with a new rubber o-ring seal.  Ive checked and re-set the floats a while ago but this shouldnt really affect idle or low load. I think I'm just going to try a few different idle jet sizes in 0.05mm increments and see if I notice anything .......  

[mangocrazy]

I have no Lancia-related information, but I do know that carburetted motorcycles from the late 80s benefit from larger idle/pilot jets and probably also main jets. My 1988 VFR750 was much more responsive when I went up one size on the pilot jets.

[smithymc]

My primary stage was increased by the Aldon  guys following the rolling road session. Now if I can just find the paperwork........

Mark

[JohnFol]

I've something in the back of my mind that bigger jets are the way forward as petrol is more "diluted" that when the cars came off the production line. Increased jets compensates for this. however .. . . I can't find the original source of this so anecdotal but interested if anyone else remembers the article

[capriblu]

Update

So with 20 litres of fresh Shell Optimax with a splash of Millers VSP I set about trialling different jet and air corrector cap sizes. 

Before my new items arrived I had already tried running the car with a spare standard 0.8 secondary idle jet on the primary side.  This made a noticeable difference to pick-up and general feeling of responsiveness from low engine speeds but obviously a bit of a big jump from the 0.5 standard jet size.

I tried the same experiment with a spare carb (both DAT 2/250s) and found exactly the same behaviour.  As well as the general difference in feeling of responsiveness when actually driving then, again for both carbs sudden blipping the throttle at rest with a standard 0.5 idle jet (I tried two different 0.5 jets just to be sure) seemed to be met with a very slight but nonetheless discernable fluff/miss.  This disappeared with the 0.8 jet.  (Ignition fine and timing checked).  I was still able to keep CO at idle reasonably steady at around 2.5/3.0%.

So my new jets and air corrector caps arrived.  (About £30 worth from Eurocarb).

Firstly I tried just changing the primary idle jet.  A 0.6 made a very big difference over the standard 0.5 but car still didn't seem to pick up just quite as well as a 0.8.   Then tried a 0.7 and this felt good. Perhaps a 0.65 would be optimal.

Subsequently took a punt with a selection of the few items that I purchased and went for this combo -

Primary Idle   0.7 instead of 0.5 standard
Primary  Main  130 instead of 120 standard,  kept standard F30 Emulsion Tube,  Air Corrector Cap 160 instead of 170
Secondary Idle 1.0 instead of 0.8 standard  (doesn't seem to be anything available between 0.8 and 1.0)
Secondary Main 155 instead of 140 standard, kept standard F30 Emulsion Tube,  Air Corrector Cap 225 instead of 240

With the above the car is absolutely transformed.  Absolutely no wooliness around transition from first to second choke and just seems smooth and strong throughout engine speed range with only a slight second choke kick which just suggests better power lower down rather than any loss at the top. 

A few short speed runs on some familiar stretches confirmed that the car is noticeably swifter and seemingly freer to head towards redline.

I could "back-off" from this combo slightly to see at what point performance/response starts to fall but for the time being I'll stick with this and see how the car performs on longer runs.  Hopefully MPG will still be sensible.  I checked the plugs after a 30 minute run and all nice and light brown.

I always felt the fuelling on the 2 litre cars to be marginal and this along with the advent of current ethanol containing pump fuels probably means the original standard jetting is now seriously inadequate.

Really pleased - car is just so much better and quicker!

I had an early F/L  HPE 2000 as a daily over 25 years ago and this drove similarly.  All the other 2000 Betas that I have driven have suffered from very slight first to second choke "fluff"to some extent. This effect could often be eliminated by retarding ignition very very slightly but at the loss of top-end performance.  Shortly after I bought my HPE Chris Bastow/Betacar rebuilt the engine with HC pistons - I'm wondering if the Carb was re-jetted as well!

[mangocrazy]

Excellent stuff! I will at some point be replacing the standard Weber on my Spider 2000 with a pair of DCOE 45s with 36mm choke, but until that happy day I think that uprating the jets as you have done will make the car much nicer to drive. Where did you source the jets from?

<Edit> - Just re-read your post and noticed you used Eurocarb. I'll speak to them in the morning.

[JohnFol]

Just found this useful calculator.  Also has good descriptions of what the effect is of increasing or decreasing values (ie smaller choke)

https://www.carb.parts/calc

[mangocrazy]

I'm resurrecting this thread as I have the jets that capriblu recommended ready to go into my DATR carb, currently stripped down on the bench. My problem is that I can't see where the jets are in the carb body. The main jets are (I believe) located underneath the emulsion tubes but I can't see any way of getting them out from where they are buried. Similarly, I have no idea where the idle jets and air corrector jets are located or how to remove/replace them.

The carbs are currently in the state pictured in my recent thread in this section.

All help gratefully received...

[HFStuart]

When you unscrew the emulsion tube it usually comes out with the main jet still attached to the bottom of it  - the air corrector is on the top that's the bit with the screwdriver slot in it. They can be a pretty stiff fit and you may not initially realise that it's three items rater than one.

The emulsion tubes are the inner brass screws  - the idle jet holders are the outer screws  - remove them and again the idle jets should come out with them, occasionally they get left behind in which case a small drill or rod can be used to wiggle them loose before retrieving with needle nose pliers or in your case turning the carb upside down.

These photos show it quite well

https://www.flickr.com/photos/55777341@N00/5464599813

[mangocrazy]

Fantastic stuff - thanks so much. I would never have known there were so many parts ostensibly in one. All the bits are in the ultrasonic tank (again) so that may very well shake them loose...

Thanks again.

Graham

[Neil-yaj396]

On and off as detailed in several threads my car ran like a dog and I'd always planned to change the jets. Once the carb was fully rebuilt all these issues seem to have disappeared even though the original jets were just cleaned and replaced. I think a lot of problems come from the many drillings in the carb body that get blocked. Hopefully your ultrasonic cleaner is industrial enough to have shifted everything.

My Coupe did 1200 miles in 3 weeks totally glitch free and now runs very smoothly, particularly during motorway driving, which it didn't do before.

[JohnFol]

I took Capriblu's advice and just swapped my "lucky dip" parts for the ones he recommended. Definite improvement.

Sourced from https://www.dellorto.co.uk/ in Pangbourne, Reading. Just a FYI, their emulsion tubes are about half the price if you buy from their eBay store rather than their own web site. https://www.ebay.co.uk/str/eurocarbdellortoandwebercarbs

[peteracs]

My experience with the 1600 DATR is that it works fine as standard. It did have an Ultrasonic bath and getting the float level correct has been a bit hit and miss, but the engine does not hesitate etc and if anything runs a bit rich which is most likely float level related.

[mangocrazy]

I'd read Capriblu's comments and suggestions and thought 'what have I got to lose?' - increased fuel consumption, perhaps. His setup was the same as mine - S2FL Spider 2000, and I'd always noticed the symptoms he was describing so I decided to give it a go. I believe that 2000 and 1600 DATR are jetted differently, so that would affect the end result. Taking the carb off for the jetting changes and ultrasonic bath has also exposed a number of other issues that needed fixing, so if only for that it's been a worthwhile exercise.

Once the car is (eventually) running again I'll report back on findings...

[capriblu]

All the later 2.0L Carb betas that I have driven have to some greater or lesser extent suffered some discernible fluff/wooliness around the transition from first to second choke (with ignition timing at nominal settings).  I don't think the jetting on the 34 DAT/DATR type carbs was very different if at all for the 1600s so might explain why this common issue seems to just affect the larger capacity engine?

Another albeit minor factor compounding the above is that modern E10 fuels will require typically 4-5% richer fuel/air ratio settings than ethanol free fuel.

Have taken my car on some good long runs and trips over the last 12 months on the jetting combo that I posted above and can report that car continues to perform much better and more smoothly.  Fuel consumption certainly hasn't suffered, if anything I'd say it seems slightly better than previously; even on "spirited" runs I estimate I'm seeing at least 27 Mpg. 

[JohnFol]

I've gone for your recommendation and had the car at L&M to get timing done, check carb and a few other bits. Agree it drives much much better as a result (and thanks to L&M), however I did have a question. If there is a richer fuel delivery due to jets, and you then apply choke, doesn't that have double the effect on the mixture, i.e. over-choking?

[peteracs]

Hi John

Are you confusing cold start choking, where a flap comes over the primary choke tube, with the two choke tubes?

Peter