Pursuing Weber 44 IDF Perfection......(Pipe dream?)

[RandyV]

First.....details.....

'56 ragtop
2085cc (78.4 x 92 thickwall)
SLR XR292 cam
Scat 1.25 (1.33 actual) rockers
.520 lift at valve, roughly 292 duration (253 @ .050)
Brothers VW heads with some Alstrup influence
40 x 35.5 mini D-port 56cc chambers
9:1 CR
1-5/8" A1 sidewinder w/ muffler
Redline 44 IDF's (55 idles, 160 mains, 200 airs F11 emulsion tubes 36mm vents)
Magnaspark2
900 ft above sea level
(all parts are new)

Second.....problem...

Driving around town she runs mostly well, except in infamous "transition"
Approx 2,500rpm (or so)
Hesitation/stutter less pronounced when cold, moreso when warmed up
Most noticeable in 2nd gear
Possibly acc pump, except holding at higher (3,000?) rpm can mimic the stutter too....but not always.
If I just run 5% throttle and never go over 2,000rpm, she drives like a finely tuned 40 horse.

50 idles (too lean)
52 idles (too lean)
55 idles (work)....where I'm at now with 1-1/4 turn out on mixture screws
57 idles (work too)
60 idles (too fat)

Interestingly all mains seem to work well enough from 145 up to 160
Same for airs.......175 up to 200 don't much matter unless I run too close together (like 160 mains and 175 airs)

Stock redline linkage is geometrically proper and synched to near perfection.
3 progression holes visible from velocity stack (i.e. 4th covered by butterfly and not cheating so appropo per Redline's suggestions)

MUCH thanks to Alstrup who I've exchanged many conversations with. He thinks I'm still a little rich on idle (though I know 52's just pop like popcorn) but likes my main stack.

John @ Redline thinks I'm too lean on idle and thinks I'm too fat on main stack. (I should be at 145 or even 140 mains)

Sera (YT: Motor7710) knows my pain....(If you see this Sera, cheers!)

Any thoughts, suggestions much appreciated. (I'll share more of my future ideas as the thread progresses)

[stevemariott]

Get a wideband / o2 sensor setup.

What’s your ignition? Elevation?

55 idles sound okay - I’d say 140 or 145 mains. I have a similar-ish combo and those jets / vents are what I’m running
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1968 Bus

[RandyV]

[Zed999]

I don't have the experience of some of the chaps on here but I'd say your venturi's are unnecessarily large for the cc's and revs your cam is capable of and there's your flat spot - the relatively small cc's / cam combo isn't producing enough air speed at transition with the large venturi size. Also you aren't getting any good from them at the top end. I'd bump right down to 32 or even 30.

My ref here is a 2020cc with a C35 and 40x35 (in a bus) that revved the nuts off (6,000+) with 30 vents and certainly was not choked by the venturis.

I would tune out the flat spot with venturi size or emulsions (though I know nothing about Weber emulsions).

[74 Thing]

Id put in larger airs to make the mains come in sooner during transition or up the floats slightly.

[Alstrup]

[RandyV]

I'm definitely not opposed to trying smaller vents, though I have to agree with Alstrup, I don't think 36 vents are the problem here and while they might help, I think there's a couple other things that could be at issue as well.....(the "future" thoughts I mentioned)....

-----------#1.) Sera (Motor7710) has gone to great lengths looking for IDF transitional answers and is still convinced that IDF's are simply just not good daily driver carbs (at least in dual form) here's what I know he's done off the top of my head......

------------------------a.) He's actually drilled the bottom progression hole (the 4 holes above the butterflies) out from .9mm to 1.0mm to match the top progression hole leaving the middle 2 at .9mm....as just ONE piece of the IDF transitional puzzle.

------------------------b.) He's literally soldered up & redrilled F11 emulsion tubes to completely rethink both the size and hole pattern of the main stack's emulsion as the mains pickup after idles.

------------------------c.) He's adjusted the acc pump bypass valve sizing manually to accomplish everything from "zero bypass" to everything in between.

***I must mention here that a lot of REDLINE'S addressing of these problems (like suggesting zero bypass valves, upping idle jet and acc pump nozzles sizes) have come about due to the change in our fuel mixes here in the states. (for the worse!!) So while some of these changes might have been taboo in the 80's they may be spot on now.

------------#2.) I will try another set of carbs soon as one thing I like is 2 of everything to quickly and effectively address a problem. It would probably take an act of God for me to prove to somebody like Redline that their carbs might have a problem but if I swap carbs and the problem goes away....well......

[vwracerdave]

Instead of getting another set of carbs you need to invest in an air/fuel gauge and stop guessing.

My 2007cc with 40X35 044 Magnum heads W-120 cam

44 IDF's 34mm venturies, 52.5i/140m/200a/F11
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[RandyV]

[Alstrup]

[Slow 1200]

what are your float heights?

[74 Thing]

[RandyV]

Float heights were set at 11mm & 28mm (from 13.5 & 22 from redline as new) when I completely disassembled them & thoroughly cleaned and tediously set everything straight on them.

Larger airs only coincide with larger main to bring mains in sooner. I’m technically there already. I still haven’t tried “new school” (like a 175 main & 220 air) but I just need to get around to finding such large jets. 🧐

Another thought (though wouldn’t solve my situation entirely) is that with stock bypass valves, I definitely don’t have squirt at small hit if the throttle. I know that Sera has played with everything from stock bypass down to modifying his by pushing down to 020 sizing bypass (which he didn’t like) but I definitely don’t have squirt upon immediate depression of throttle.

https://youtu.be/MapoC1cS5Pc

I need to speak to John at redline again but I believe he suggested ZERO bypass and I’m not sure that isn’t overkill with potential for bad results but one way to find out. (There are technically various bypass cutoff sizes too or am an be modified as sera has done by driving the wedge stopper down further to the desired height).

But again this wouldn’t be 100% of my problem because I still have a miss/stutter at fixed throttle position around 2,500-3,000rpm which is more related to one of the circuit flows. (Idle circuit I suspect but just my guess)

[BFB]

[W1K1]

[oprn]

I am going to throw my support behind Racerdave, W1K1 and others with getting a wideband on there so you can actually see what is happening right at the time and in place. By the sounds of it you have spent more than enough on jets and bits already to have bought a wideband!

I cannot comprehend the mentality that says spend $4000, $5000, $6000 on an engine but don't spend the $300 that it takes for the tool to make it all run right!
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[74 Thing]

Airs:
http://vwparts.aircooled.net/Weber-IDF-IDA-Air-Jet-77401-p/77401.htm

Mains:
http://vwparts.aircooled.net/Weber-IDF-IDA-Main-Jet-p/73401.htm

[RandyV]

While I fully understand the desire for AFR data, in this situation where it misses/stutters, I am 99% sure that all the log will show is a lean spike. (I diagnosed the same before when I had the fuel delivery problem). I can schedule another run on the wideband but I know what we’re gonna see.

It won’t be a rich condition. (We’ve already ruled that out with jetting/plug reading ***AND*** innovate wideband AFR logs).

And when it shows the spike, it also won’t tell you which cylinder is the culprit. (Or if it’s just 1?)

So then what do you do with a spike on the screen? (Remember, any more playing with jets is really just futile as we already know floor/ceiling and outside of that threshold means something is wrong in the carbs and the AFR can’t tell us what that is)

FWIW, I haven’t spent dime 1 on jets yet since I am amongst friends with jets….lots of jets. Thus the literal floor and ceiling knowledge of idles, mains, airs and emulsion tubes.

Also….we do know where 44 IDF’s transition from idle to main circuits based on other’s (Sera) research. And for anyone who doesn’t know, if you ever want to find out, pull your main stack entirely and drive around very slowly climbing in rpm. You’ll find out in short order.

And lastly…yes I did say in this thread…..12 at idle, 13 @ WOT, 14/15 at cruise. No need to read the other thread. We know the jetting threshold.

[stevemariott]

[74 Thing]

OK, if you don't want to spend money on jets and a AFM it is your money.

If you change to larger airs the mains come in sooner and will help with that lean transition. The larger mains will also lean out the upper end and therefore the AFM will come in handy to up the main jets so you are at your target AF ratio at WOT.

If you want to know what is going on in each cylinder you can always add an O2 bung for each cylinder.

You can also throw it on a dyno and use their AFM and the load test of the dyno and bring you friends stash of jets to jet it out. I would measure the jets first so you are making jet changes correctly.