IDFs are very lean at Idle

[Scrapefest]

Hi I am just trying to set up a pair of 36 Weber IDFs on a fresh build 1904.

The problem I have is at Idle the AFR is in the 20's I have taken the carbs off several times , I have closed the air bypass screws, checked the throttle plates are a close fit, I can get a 0.05mm feeler gauge past the plates set so that the engine idles at 900rpm. I can't see any wear on the carb body. The choke mechanism was missing parts so I blocked off the lower outlet.

I have set up other twin IDFs and the idle is often around 12 afr , and as a quick test I put on a spare 44idf and the idle afr was straight into the 12s.

On a light cruise I was seeing the afr in the 17s but it felt like it had a flat spot .

Any one have any ideas why the idle is so lean.

The current jetting is
52 idles
135 main
180 air
30 Venturi

The engine is
1904cc
Heads AA 043
Engle 110 cam
Bosch SVDA Distributor
Vintage speed sport 130 exhaust

[volksworld]

I'd try 55 or 60 idle jets

[oprn]

What is the ARF at light throttle? Say 10% open still on the transfer ports? 45 - 50 mph steady cruise. Are they the good Italian carbs with 5 transfer ports?

Just some after thoughts, 36's might be a bit small for that engine but that should not effect the idle. Valve overlap might though.
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Our cars get old, we get old but driving an old VW never gets old!

[modok]

How many turns open are the idle mixture screws?
They are fine thread so up to 6 turns out is ok

Idle jets should be 57-62 for 13-1 cruise

Or 50-52 if you want to run lean lean for max mpg

To cruise lean and idle rich you may need to enlarge the hole the needle goes in

[Slow 1200]

If it's idling smoothly at 20 AFR you must have a pretty hefty ignition system or the measurement is wrong

[oprn]

[Scrapefest]

OK, embarrassingly I think I lost my mind with this. I started with 55 idles road testing it was rich in the 11s, that's why I fitted 52 idles which gave high 12s afr even though it drove better with the 55s, that's why I spent time thinking it needed the 52 idles.
It didn't help that it is not my vehicle and the suspension is awful so road testing was difficult.
I put the 55 idles back in and the afr changed to 12 at Idle . I've not had chance to drive it yet.

The carbs are Italian IDFs so hopefully it was just my mistake rather than a problem with them as I have another pair on my Bay which drive very well.

Thanks for the help.

[modok]

Oh, that sounds workable.


I ran several sets of these, and sometimes one or two of the idle mixture screws ended up basically open all the way, and yet they ran great and it was the least of my problems, and I was used to that as a lot of the carbs made in that era were that way........you know... the pessimistic view was the carb engineers were trying to protect mother earth against morons with screwdrivers, but at the same time, some of the most accurate carburetors ever made, once you figure them out and pry the anti-tamper covers off the adjustments and make a few small alterations.


44idfs are just very different, they have enough range built in you can run methanol or whatever, which is good, but touchy adjustment, as in.... the difference between too rich and too lean idle could be just one turn of the screw.

[Scrapefest]

I am back on this now after stripping the front suspension to grease it up, now it has some movement.

With the 55 idles it drives very nicely, no flat spots. However at light throttle in 4th at 40-50mph I am seeing afrs in the 14.4 to 15.6 area. This was on a short test route where I have about 1/8th mile to put my foot down , the rest is slow 30mph stop start roads, I see afrs in the 17s here.

Before I go testing further afield, am I essentially cruising in the ' Death zone' if I am seeing afrs in the 15s or am I ok if it is above 15.1.

Thanks.

[ORANGECRUSHer]

Scrape, there is a thread I can link you too that may set your fears to rest. I'll try to find it. It's a long read, but it has a lot of juicy stuff.

When you at cruise which is to say your maintaining a higher speed with very little throttle input you want a lean mix for economy. The tricky part is getting WOT and idle where you want it and then also having that lean cruise. I was there once and then I radically changed my intake and I'm where you're at now also.

When I've gotten to a point where I don't know what to do I start from scratch again.
-pull the main stack and just run on the idles. drive it and take note of how the accelleration feels. It should get to between 2500-3000rpms and then fall on it's face because no mains. Try at least three idles going in both directions until you find one that has the best feel.
-put your main stack in with a really big main and drive it through the transition. This will tell you where your mains are kicking in. It won't be good on the mains the point being to make the transition easy to feel. Then dial in your air jets so that the flat spot at the transition just goes away.
-Next it's time to dial in your mains which should be pretty simple especially if you have a AFR gauge.

remember:
If you go leaner you need to dial back timing and vice versa.
Every time you change a jet or change timing you need to readjust the idles.

I feel like maybe one of your issues with that 52 idle was you didn't pull your timing back to compensate for the quicker burn

Just as rough comparison, I have a 2110 (not that much bigger) but I'm running dual44's. I'm undecided atm on 52 or 55 IDLES. I have a 145 main and with a 190 air I have a nasty flat spot with the 52s.
I put my 55's back in this morning which makes starting a whole lot better when cold, but I'm getting a lot of sputter until I get on the mains. The transition isn't as bad. When I'm cruising I can hear a very low second exhaust note(hardly perceptable) going in and out and I'm not sure what to make of that. I think 52's are where I need to be and maybe even possibly 50's. If I can get my airs changed out soon maybe I'll find out. I'm not sure how that all translates to a single carb setup. Seems like it's be about the same jetting wise. Only one cylinder at a time can eat...
_________________
Brian H.

OrangeCrushERBerrien Warrior-2.4L Quad4-2x3 arms-1.5Fox coilovers-094-930CVs
LAZY MARY1970 Baja 2110cc-82mm CB forged crank-AA pistons/cylinders-Grant rings-1.1 vw rockers-CB serpkit-CB chromoly PRs-CB maxiflow filter pump-wix51515 filter-Dual 44IDF-cut/turned front beam-AEM wideband-Auber CHT-Donaldson Dual PowerCore filters-custom AL air boxes

[ORANGECRUSHer]

This is the thread that always helps me.
https://www.thesamba.com/vw/forum/viewtopic.php?t=293837&highlight=wideband
_________________
Brian H.

OrangeCrushERBerrien Warrior-2.4L Quad4-2x3 arms-1.5Fox coilovers-094-930CVs
LAZY MARY1970 Baja 2110cc-82mm CB forged crank-AA pistons/cylinders-Grant rings-1.1 vw rockers-CB serpkit-CB chromoly PRs-CB maxiflow filter pump-wix51515 filter-Dual 44IDF-cut/turned front beam-AEM wideband-Auber CHT-Donaldson Dual PowerCore filters-custom AL air boxes

[ORANGECRUSHer]

The thing that always stuck with me is someone saying most people's inclination is to fix driveablity issues with richer jets and then advancing the hell out of it. I think I fell into that group. I always had soot sneaking out from the joints in my exhaust. Now the holy grail for me is trying to find a way to go leaner and get the driveability I want. I still haven't figured it out.
_________________
Brian H.

OrangeCrushERBerrien Warrior-2.4L Quad4-2x3 arms-1.5Fox coilovers-094-930CVs
LAZY MARY1970 Baja 2110cc-82mm CB forged crank-AA pistons/cylinders-Grant rings-1.1 vw rockers-CB serpkit-CB chromoly PRs-CB maxiflow filter pump-wix51515 filter-Dual 44IDF-cut/turned front beam-AEM wideband-Auber CHT-Donaldson Dual PowerCore filters-custom AL air boxes

[Scrapefest]

ORANGECRUSHer thanks for the reply.

I have read the Wideband thread and refer to it now and again but sometimes it's hard to pick out the exact solution to a problem. Such as the death zone, should it never run between 14.5-15.1 or is it ok at light load. Is 15.6 ok or will the engine get hot.

In this case I have built an engine for a friend and want to give it back to him tuned safely so he can run it in without cooking it, when he collects it he will be driving 50 miles to get home .

When I tried the 52 idles the richest I could get the idle was in the 15s and driving around it also was in the 15s and seemed to be getting hot . How much timing do you think needs taking out to make it run better.

[ORANGECRUSHer]

That's what I'm still figuring out. Technically, if your underway and light load 15's are no biggie. Some would say you could be in 16's and 17's cruising. But underload I think is where you get into problems. Do what you need to get 12.5-13's at idle. I had a very hard time getting idle leaner. It seems like there's a jump. But then again my sensor burned up last week and I haven't had a good reading in a week.

Maybe spend a little time going by feel and put a piece of tape over the AFR. Put a couple idles in and adjust them best you can and then take note what they're doing. Then depending on if you went richer or leaner change the timing by a degree or two and make a note which is better.

It seems like over kill but I really think it's smart to grab a cheap notebook and make a journal or as car guys call them, a log. I get forget what I did two steps ago much less exactly what was happening.

If you want to start that on here I'll try helping you. Hopefully others will correct me if and when I'm wrong. I love a good tuning thread.
_________________
Brian H.

OrangeCrushERBerrien Warrior-2.4L Quad4-2x3 arms-1.5Fox coilovers-094-930CVs
LAZY MARY1970 Baja 2110cc-82mm CB forged crank-AA pistons/cylinders-Grant rings-1.1 vw rockers-CB serpkit-CB chromoly PRs-CB maxiflow filter pump-wix51515 filter-Dual 44IDF-cut/turned front beam-AEM wideband-Auber CHT-Donaldson Dual PowerCore filters-custom AL air boxes

[modok]

Are you having trouble figuring out what you want?
Just read my first post again.

If you want max MPG, jet it as lean as you can get away with, and that may depend on your ignition system somewhat. If it's not lean enough for your liking, work on your ignition system more until it is.

If you don't care about maximizing MPG, then jet it for 13-1


MPG nuts....it's like an incurable disease that you either have it or you don't.
But everybody is different, right? I think so
Maybe you are one of the rare "MPG non binary" types

[ORANGECRUSHer]

omg
_________________
Brian H.

OrangeCrushERBerrien Warrior-2.4L Quad4-2x3 arms-1.5Fox coilovers-094-930CVs
LAZY MARY1970 Baja 2110cc-82mm CB forged crank-AA pistons/cylinders-Grant rings-1.1 vw rockers-CB serpkit-CB chromoly PRs-CB maxiflow filter pump-wix51515 filter-Dual 44IDF-cut/turned front beam-AEM wideband-Auber CHT-Donaldson Dual PowerCore filters-custom AL air boxes

[Murt]

Hi @Scrapefest
I have been watching this thread with interest. I have been trying to set up my new engine. and gradually making some progress. What confuses me somewhat is all the talk about AFR's. Yes, I understand the technology somewhat, and learning every day. But is what we're saying here that to own a VW with any sort of modifications, you need to have an AFR system fitted ?
I know it sounds very Old technology, but I have been fannying around on mine lately, yes it's a bit painful, but with just a screwdriver and a snail, linkages on and linkages off lots and lots and lots of adjustments and runs out.

I have Dual Italian Weber IDF36's as well. Straight out of the box, cleaned thoroughly, and floats set to 9mm. Originally came as F50's/135 mains/52 Idles/220 airs.
The current jetting I have after some experimentation is :
F11 Emulsions
47 idles
125 mains
220 airs
30 Vents

My point being, is that, I have spent a fair few dollars on buying various jets etc, and at the moment can't really justify spending a few hundred more installing a permanent AFR system (That's not to say it's not in my future ) but just not now. What I have in MY engine above is what is currently working for Me.
Bus Idles very nicely, Picks up on the throttle nicely, and I don't notice any flat spots when driving.
I'm 100% sure that I will still need to tweak it some more I know jack sh*t about carbs apart from what I've read, but learning everyday. What I am trying to do is perfect an 'Ear' and trying to understand what my engine is telling me

PS. Using 99 Octane Petrol, and don't give a S**t about MPG

The Engine is
1800cc (74x88)
Heads AA 043
Engle W100 cam
Magnaspark II Distributor
CSP 38mm Bus exhaust, with J Tubes
_________________
1966 VW Beetle ‘Jules’
1967 Kombi Splitscreen ‘Barney’
2018 VW Caddy Maxi R Line
2017 Golf GTD saloon
2008 VW EOS 2.0 TFSi

[SGKent]

I think AFR is an abbreviation that is being used in this post for "Air to Fuel Ratio," and not an air to fuel gauge. That would be a wide band oxygen sensor combined with a Digital Air Fuel Gauge, which would read the amount of oxygen left in the exhaust gasses, and that reading would then be converted by the digital gauge to an approximate air to fuel ratio, although quite accurate compared to say trying to read spark plug colors with modern fuels.
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"Most people don't know what they're doing, and a lot of them are really good at it." - George Carlin

[Murt]

Thank you @SGKent.
Yes, and I don't want to hi-jack @Scrapefest's thread in any way, but I have been trying to understand and assimilate all of this including the Stoichiometric aspects and the current fuels on offer over here in the UK.

My point was is it all really necessary ? would not a really good old fashioned mechanic not be able to use knowledge and experience to get the carbs about right ? not saying perfect as in 110%. I just think that the Alfa Romeo dealerships of old would have serviced their everyday cars the 'Old fashioned Way' ?
I also want to know whether the use of this technology may it be capable of displaying in either AFR or Lambda like an Innovate kit for example, is just another distraction, and taking away the pleasure of driving our vehicles ?

Please don't get me wrong, I am not a Luddite, and in the greater scheme of all things VW, I know nothing, but I welcome any new technology, as long as it serves its purpose, and I sincerely hope that @Scrapefest, finds that sweet spot on the 36's that suit his engine, and wish him luck.
_________________
1966 VW Beetle ‘Jules’
1967 Kombi Splitscreen ‘Barney’
2018 VW Caddy Maxi R Line
2017 Golf GTD saloon
2008 VW EOS 2.0 TFSi

[Scrapefest]