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Author Topic: Jetting on standard DATR/DAT type Carb  (Read 112 times)
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capriblu
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« on: January 09, 2021, 09:19:06 PM »

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 .......... Huh?  
« Last Edit: January 09, 2021, 09:54:10 PM by capriblu » Logged

!980 2.0 Coupe - Owned since 1990
peteracs
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« Reply #1 on: January 09, 2021, 10:04:03 PM »

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
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Beta Spyder S2 pre F/L 1600
Saab 9-3 1.9Tid Cabrio
capriblu
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« Reply #2 on: January 09, 2021, 10:28:13 PM »

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 .......  
« Last Edit: January 09, 2021, 10:32:01 PM by capriblu » Logged

!980 2.0 Coupe - Owned since 1990
mangocrazy
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« Reply #3 on: January 12, 2021, 05:29:50 PM »

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.
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1980 Lancia Beta Spider 2000 (S2FL)
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« Reply #4 on: January 12, 2021, 08:02:24 PM »

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

Mark
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JohnFol
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« Reply #5 on: January 13, 2021, 05:00:44 PM »

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
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