Weber IDF progression phase

[Brit01]

DHLA pair was great. Even the mixture got little lean and jumped to lambda=1 range when accelerating lightly, it doesn't bog down like IDF's. It just goes.
With IDF's, when mixture goes even near lambda=1, it dies and stutters like mad and this lasts long.

I have another question.

I'm using DRLAs and would like to know what pump jet size you used and mains.

I have a box of idle jets, 52, 53 and 55.

Always used 142 mains.
52 idles is good in summer. I increase it to 53 in winter. 55 feels better but as you said my AFR is rich 10-11 and blackens the plugs in no time.

Even though I have an Alfa boxer I think we're along the same lines.

I have 33 pump jets and will increase these to 35's this week from a local mechanist who made them for me.
Had a little flat spot under acceleration after opening my air box a little more.


If you need 53,54 and in between sizes, I know a guy on an internet auction site who sells them in Italy.
If Guy doesn't mind me posting the seller or I can PM you.

[Urbancamo]

Might I ask what your initial timing is set at?
While you want 34-36 total with large cams initial will want to be 18*. Lazy low speed caused by big cams will induce large throttle openings that uncover all of the progression holes before you have enough air flow to pull fuel.

You mention increasing idle air bleed. You won't drill the emulsion holes in the 55 jet itself but the master bleeds in the main carburator body. This is common practice in high performance applications. With 55's i assume you have little idle screw opening. Adding air bleed will allow a larger screw opening and lean the cruise richness you are having with the 55's.

Hi robert:

Initial timing is 10 deg BTCD and maximum advance approx. 32 degrees BTDC. Im stuck with that because any more advance will produce detonation wery easily in situation that i describer earlier in this topic.

And cams are stock 2-litre cams, so no long-duration race cams here.

And you're right about the air bleeds. I got totally mixed up.

DHLA pair was great. Even the mixture got little lean and jumped to lambda=1 range when accelerating lightly, it doesn't bog down like IDF's. It just goes.
With IDF's, when mixture goes even near lambda=1, it dies and stutters like mad and this lasts long.

I have another question.

I'm using DRLAs and would like to know what pump jet size you used and mains.

I have a box of idle jets, 52, 53 and 55.

Always used 142 mains.
52 idles is good in summer. I increase it to 53 in winter. 55 feels better but as you said my AFR is rich 10-11 and blackens the plugs in no time.

Even though I have an Alfa boxer I think we're along the same lines.

I have 33 pump jets and will increase these to 35's this week from a local mechanist who made them for me.
Had a little flat spot under acceleration after opening my air box a little more.


If you need 53,54 and in between sizes, I know a guy on an internet auction site who sells them in Italy.
If Guy doesn't mind me posting the seller or I can PM you.

I don't know exact specifications in my DRLA case bacause car wasn't mine. I remember that idles were 60 in size, but the engine was tuned 2-litre Fiat Twincam.

I can find 52 idles for IDF's easily. No need for DRLA jets. Thanks for offer.

I am interested which range your AFR's stay Brit01, while driving steady speeds, like 40, 60, 80 and 100 km/h. And how high the AFR jumps while you try to accelerate lightly/semihard?

I wonder, how these Alfa's perform in stock condition with DRLA carbs? Do they stutter while pressing accelerator pedal lightly or are they adjusted little rich side in the factory?
Haven't driven any car that have factory dual carbs...

My DHLA case was, i believe with 5 progression holes, that might explain real good light/moderate acceleration AFR readings and good feeling.

Tommi

[Brit01]

I am interested which range your AFR's stay Brit01, while driving steady speeds, like 40, 60, 80 and 100 km/h. And how high the AFR jumps while you try to accelerate lightly/semihard?

I will let you know more once back up and running after it's rebuild.

Before rebuild - cruising at 100/120 km/h AFR was around 14.0-14.7.

Idling at 13.1 - good compromise. Peak idle rpm achieved with this ratio. Any lower and revs tend to drop and gets too lean. Boxer likes to be on the rich side.

When accelerating hard it drops to about 11 (pump jets actioning) then settles to about 13.5 on the idles cruising before the mains kick in.

If you get it right there should be no stutter/hesitation. They are very good carbs.

[Urbancamo]

Little improvements for progression.

Today i installed 52 idles for IDF's. Went to test drive and...

Then i remember that sizing up the air correctors could bring up the mains earlier. Last lambda run showed that micture was bit rich on upper rpm's so this was desirable modification anyway.
Old A/C's were 190, i put 200's in place.

These modifications combined gave very reasonably progression phase. You can now "feather" throttle eg. at 80 km/h speed if you want. It still gets little lean, but anyway it doesn't die completely and sneeze anymore.

So i'm real satisfied. Small changes definetly made the car much more drivable.

-T

[robert kenney]

Same correction I made on the 2L I built for my sis to better a lean progression. Remember to watch main jet running conditions for lean out at high rpm. I went up 5 on main fuel when I upped the AC's 10. The AC up sizing will lean the main circuit.

[Brit01]

cry

Now my lambda is not working correctly, or the control module.
Had the lambda cleaned, but was not really sooted anyway. Looked almost new.

The gauge jumps from 10 to 20 and flashes. Maybe the unit/gauge is underpowered or a bad connection somewhere. Have to get my DMM out and check all the wiring and voltages.

Tech support told me it would show #3 on the gauge if the sensor was faulty.

[Marc]

I think you have chokes that are too small ,try some 34mm in that set up.55 idle progression,f11 emulsions...

[Marc]

I have the same issues with my car,40/80 cams,40idfs,34mm chokes,headers,plex 201,.I will try the 52 idles,have 55 installed,130/main,175 air,f-11 emulsions.Same progression issue,stumbles on transition.If any of you have John Passini's weber book,page 56/57 specifically talks about dual carb fiat124's,after setting up the fuel mixture,open all the air bleeds up to half turn out and lock them in place.I wonder if this was set up by the factory this way?Guy,with all the information I have,I have never seen the exact jetting that came on CSA's like yours.1608 jetting is published,but not 1756.What exact jetting was on your car when you purchased it?Are the air bleeds supposed to be open?Itried it and it idles smoother,but has made the issue worse or more pronounced on transition.
I have plenty of jets,135 mains seem to blacken up fast,although it has great power,it should be about right with 135 mains although 130 seem to be better at prolonging the plug fouling issue(still has safe range colour on a snot check).By the way,same issues on a high compression 1800 i just installed,using the current head carb cam setup.I run straight Cam2 fuel 99 octane,no detination ever.

[Urbancamo]

And i wonder would factory Spiders run at LIQUID gasoline because they had 55 idles installed? Or is the idle air hole size changed on the IDF body?

I've never driven any car with factory dual carbs, but i believe that kind of stumbling is not accectable on production car. So what is the way they have cured this problem?
Comments anyone who has factory dual carbs on their car?

This car i deal with, has newer IDF40 70-series carbs, which are i believe made in Spain.
Car has now reasonable progression, it's much better than before but it's still there. But it's drivable and not as annoying as it was before.
Compromises, compromises...

[Abarthnorway - Remi L]

Hi Tommi!


I have not had a car with IDF as std fitment, but have played around a bit with the Original Solex ADDHE/Weber DCOE on 130 TC engine - and 44 IDFs and 45 DHLAs on non standard engines.

The progression on the Weber is a bit better than the Solex - I suppose it has to do with an extra progression drilling. If my memory serves me correctly they both had pre drilled idle air holes in the body.
The progression is acceptable on both and much better than any IDF fitted engine I have driven. The DHLA was the best of the the sidedrafts, but only when I changed the idle air tube for a rather rich one.

I agree that the IDF is the worst of the bunch - only way to get smooth drivability in my experience is to beef up the idle jet (55 or 58) but it runs to rich at low speed. This is for 44 IDF. I suspect the DRLA is better in that department - never tried.

I am really keen to try to drill out and tap the idle air bleed hole for fitment of an air jet, to make it more suitable for various engines sizes/tune. I really consider that the only doable option. To drill extra progression holes is not something I would dare to experience with to be honest.


Best regards

Remi Lovhoiden

[Urbancamo]

Thanks Remi for your detailed post! Can you remember the 130TC Weber serial number, like 18 or 144 etc..? Weber has changed progression drillings thru years, and so has Dellorto too.

I drove in the past universal performance DHLA pair wich was fitted with WB lambda, i noticed immeadiately that even reading jumped a bit lean on light/medium acceleration, there was no such a markable hesitation than IDF. Very noticeable difference.

I'm glad to see i'm not the only one who has struggled with this problem.

[Abarthnorway - Remi L]

Hi Tommi!

I will check the numbers next week as I have some time in the garage then. Regarding the Solex version the very much used Haynes Manual states tipo 27 - and most other sources as well - while it in fact it is 37 stamped on the bodies (at least the 5 pairs I have.....) The 27 is a very different carb to the 37 - I have learned the hard way when ordering jets etc.
Come back to You next Week.

Remi Lovhoiden

[Brit01]

I drove in the past universal performance DHLA pair wich was fitted with WB lambda, i noticed immeadiately that even reading jumped a bit lean on light/medium acceleration,

strange...(before my WB lambda control unit died cry) I found it went rich (DRLA though).
As it should due to the pump jets taking action against the influx of air when opening your throttle.

Maybe your pump jets were set up incorrectly? This is their sole purpose to prevent the mixture from going lean under acceleration.

[Abarthnorway - Remi L]

Hi!


This interesting thread is about to drift off into something not directly related to IDF`s - start a new thread???

Anyhow:

I drove in the past universal performance DHLA pair wich was fitted with WB lambda, i noticed immeadiately that even reading jumped a bit lean on light/medium acceleration,

strange...(before my WB lambda control unit died cry) I found it went rich (DRLA though).
As it should due to the pump jets taking action against the influx of air when opening your throttle.

Maybe your pump jets were set up incorrectly? This is their sole purpose to prevent the mixture from going lean under acceleration.

I suspect that the phenomenom Tommi refers to is the hesitation when adjusting the throttle slightly - not a hesitation when slamming it. The squirt of petrol delivered by the pump jets is too short in duration to cope with light acceleration. In my experience the lean mixture in this phase on Dellortos is down to the idle emulsion tube that needs to be richer. This has been the case for the two cars I have set up with DHLA`s: one tuned 1290 sohc(40`s universal) and a tuned130 TC Abarth(45`s) -


Remi Lovhoiden

[Marc]

Ok, I found that using a 55 idle,135 main,f-11 emulsion,200 air seems to work best.still had a tiny bit of sneezing under progression,fitting weber filter screens to my velocity stacks solved the issue.Engine is 1756,10.8 pistons,43/36 valves,40 idfs,Fiat waffle intake,headers,plex 201 ignition,40/80 cams.gained alot of power by switching to 34mm chokes.The progression phase seemed to get better with the 34mm chokes.Problem in the USA is that none of our cars came with dual carbs.Left hand drive means no DCOE's because of the master vac unit is in the way.We don't have the selection of parts from engines that were never imported to the US.1438/1592/1608/1756/1995 are our choices.No 1585.all 1800/2000 engines were only 8 to 1 compression, hence,not many dual carb set-ups.My carbs are 40 Idf 70 series.I wish Guy would post the stock jetting on CSA,never seen the jetting for a 1756 engine with dual carbs.At least this would give a starting point.