Weber IDF progression phase

Road-race engines and ancillaries - general discussion
Abarthnorway - Remi L
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Re: Weber IDF progression phase

Post by Abarthnorway - Remi L »

Urbancamo wrote: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.

Hi Tommi!


The Weber fitted to the Ritmo 130 TC were tagged (40) DCOE 146 - Tipo 50
The carbs have 5 progression drillings.

Set of Weber 40`s
Set of Weber 40`s
Weberpanoramafront.jpg (13.09 KiB) Viewed 6093 times
Progression drillings
Progression drillings
Weberenrichment.jpg (7.62 KiB) Viewed 6093 times

Best regards

Remi Lovhoiden
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Marc
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Re: Weber IDF progression phase

Post by Marc »

Solved the problem with the Progression Phase.Switch to 34MM CHOKES,32mm is way too small and will cause the issues we were all having with the idle progression phase.
Urbancamo
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Re: Weber IDF progression phase

Post by Urbancamo »

Nice to hear you found a solution on this dilemma. How much better it got with choke change?

T
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124AC
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Re: Weber IDF progression phase

Post by 124AC »

Hi, sorry to mention the 'F' word here, but I found a great article for progression in a Ford article many years ago. I will see if I can find the article.

The writer detailed the process for measuring and then drilling extra progression holes matched to throttle opening. What he demonstrated was that the first progression hole was often too high, you had to get the throttle open before it came into play. This led to the stuttering and spitting. Drilling a small extra hole slightly lower allowed a balance to be achieved between the new progression hole and the idle setting.

Next problem was the lack of upper progression holes to manage the transition. Again, this could be adjusted by adding an extra hole or two at the wider throttle opening before the main jets come on song.

By drilling these holes really small and assessing the results he was able to show much better light throttle performance for road based cars.

Mapping the response on a rolling road or Lambda setup allows you to open up the holes to achieve a smooth pickup.

It was interesting to note that the bottom hole was very small, and they got progressively larger.

It should also be noted that any spindle or linkage wear makes this a pointless exercise!

I have run many Alfa boxer setups for road and track and the progression on many of these has been really good. Conversely, a mildly tuned angine with some decent porting was almost undriveable unless the throttle was half open!
Brit01
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Re: Weber IDF progression phase

Post by Brit01 »

I have run many Alfa boxer setups for road and track and the progression on many of these has been really good. Conversely, a mildly tuned angine with some decent porting was almost undriveable unless the throttle was half open
I'm interested in hearing more about your Alfa experience.

I have a 33 1.7 running Dellortos 40's with 32 chokes.

52 idles
142 mains
180 airs
.4 emulsions.
untuned - road use
balanced well

I'lll be fitting a new fuel pump this weekend as I believe my old one is failing. Failing to prime and start up after 5/6 days of standing still.
Also a lack of power under low revs, seems to be lacking fuel.
53 idles and 55 idles tried. Too rich but with the same hesitation so could all be pump related.

Have you modified/tuned Dellorto 40's on these 1.7 boxers before?

Regards

Chris
Abarthnorway - Remi L
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Re: Weber IDF progression phase

Post by Abarthnorway - Remi L »

Marc wrote:Solved the problem with the Progression Phase.Switch to 34MM CHOKES,32mm is way too small and will cause the issues we were all having with the idle progression phase.
Hi!

Not to trying to be overly critical here, but I do not understand how a choke change on its own from 32 to 34 would solve idle progression problems with the IDF. Sounds more like a jetting problem to me....

I would very much like to know how a choke change affects the progression phase in the IDF-

Thanks

Remi
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WhizzMan
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Re: Weber IDF progression phase

Post by WhizzMan »

Could it be that the chokes were so small that the vacuum at full load was really high? That would mean you would go for different main jets, thus causing progression mixture trouble? Carburetors are devices where in the end, everything influences everything, more or less. Getting a setup that works with all different RPMs and loads is difficult. Having essentially too small chokes for the engine configuration will make that even harder.
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