Ok, little background before you can help.

44 idf's - freshly rebuilt.
34mm venturi's
50 Idles
135 Mains
195 Airs
F11 Emul
Accel pump jets are 50 i believe (new style weber with non roller cam pump - adjustable)

Motor -
2L (71 x 94) 8.3: 1ish... Mallory unilite (12 deg/29 deg) CDI box, coil, etc (it aint foulin plugs with this setup.....)

CB performance TALL manifolds, and linkage.....


OK... so here is whatsup.

Idles great, played with mixture screws etc and went thru the pre-tuning procedure as listed in Bob Tomlinsons weber IDF book....

Air bleeds are .5 turns open and all barrels are flowing about the same. Idle mixture screws are i think 2.5 turns out... and thjose are the settings.

So the idle circuit seems to work OK. decent low end, Top end FLIES! but the transition is HORRIBLE. it falls flat on its face and sputters and then takes off like a rocket at WOT ( lean stumble? )

any one have any jetting suggestions for the above specs that may fix my stumle?

I have some 32 vents i can try, but have a feeling it will take away some top end....(might be OK if i pick up some more low end)

tired of fighting with them...

today, car felt shitty. it was backfiring etc... hasnt done that in a while. i am gonna change intake manifold gaskets, and see if i have an airleak...

any ideas???

You have a 2.0L.....500 ccs per clyinder & 50 idle jets.
I have a 2.7L.....450 ccs per clyinder & 60 idle jets.

IMO, you gotta run rich to get thru the lean transition stumble then burn thru with an MSD or some such. Works fer me

ill put the 55's in....

and re tune....

mallory CDI and GIANT coil dont foul plugs

I have almost the same problem with my 40's I have tried damn near every jet combo you can think of and it didn't make much of a difference. The only thing that has minimized it for me is advancing the timing a bit. If you figure it out let me know!!

im pretty sure stepping down a venturi size would be better. lets see if we can "mask" the problem with bigger fatter mixture on transition.

we tried a BIG/HUGE accel pump burst to try and make it better....to no avail

Have you thought about updating to FI? It's the latest rage.

I know my wife would kill me after dumping almost $1000 in these carbs if I didn't make them work, heh heh

I have:

Vent: 28
Idle: 50
Main: 115
Air: 200
Emul: F11

do these seem right for a 2.0L? I'm gonna drive it tomorrow now that all four cylinders are firing, and see how it goes!

Question: when you put your hand over a carb throat, should the engine rpm's slow and the car stumble? My car stumbles and almost dies when i cover the passenger side throats, but not AS much when I cover the driver side throats....has anyone noticed this?

28 vents??? wayy small for a 2l! maybe for a stock cammed one... but man, that is 1.7 jetting...

can we keep it on topic for my situation please? (not being crabby- but please ask it in your own thread)

AA, this is probably off topic, too, but smaller venturis sure pulverize the fuel better.

As a cave dweller I raced a 250 Ducati single. Granted, the 914 has 500cc cyls, but the Duck redlined at 11k rpm. I'm certainly no engineer, so don't beat me with Boyle's law, but isn't about the same pull??

Best performance was on a 30mm Dell. Different jets for altitudes, but small vents were the ticket.

edit: and green line was 6k. Just coughed and spit below that. Used a 28 on the street.

Seems like something is sticking, like the butterfly maybe. I remember having to constatnly adjust the linkage and the springs on the 40's because the springs would sometimes stick if I did not keep them imaculantly clean and the linkage would constatly move (bad roads maybe? ).
May I suggest trying smaller venturies and larger jets? Check your butterflies to make sure they are moving smoothly. And try removing each venturi and blowing hard (no friggin jokes here please) in each one to make sure there are no minute obstructions that could be blocking smooth gas flow.

i agree....

i have the smaller vents, but they tend to choke off the higher end where the motor makes its power (3.5k to 6k power band or so...)

Howie,
I remember having to change venturi sizes in the line to the race track (pushing the bug when needing to move forward) to get better performance.

Doesnt changing venturi's dictate slightly less large jetting?

as air velocity is increased, should pull more fuel in right?

AA

You need to go with bigger idle jets. I am running 65's on my 2056. If I switch to 60's I get the same flat bog in transition.

You also might want to close the air bleeds. Adding air to your idle circuit is going to make the problem you have worse.

AA;

I had/have the exact same issue with my carbs and unlike Mark, I had success going smaller with the idles.

My Specs with 44 IDFs for 2.4l (103x71) 8.7:1 CR

Vents 36
Idle 55
Main 165
Air 210
Emul f16

When I first put the motor together I did what probably many people do, I went big. Bigger motor needs bigger everything else right? I have tried many combinations but I was having the biggest stumble/backfire/hiccup during transition and it was pissing me off. I went from 65 idles to 60s. Stumble got better, but not gone. Dropped to 55s and the stumble has all but disappeared and the car pulls like a clydesdale, but it's still not quite there yet.

Brad thinks my Vents may be too large (if my 36s on a 2.4 are too big, then the 34s on your 2.0 have to be too large, right?) We are supposed to have a dyno day to try and solve these issues, but sounds like the thoughts of a few others also point to the venturis.

Should you go to a smaller vent size, and it works for you, make sure to let us know (and keep me in mind to sell those 34s!)

At your elevation, you should be jetting more fuel than air.

Changing the venturies and jets will dictate how your fuel/air mixture is used. (dont quote me on this!!!!). Venturi size does matter, but don't ask me how or why. I just know from experience by changing the sizes until finding a good match.

right... ive seen 2056's with 32's AND 34's.... my 2L is ~60cc shy of that.... so i can try the smaller vents soon enough, but i will try the bigger idles first....

AA

Should clarify my carbs are DRLA 40's with 34 vents. I am at 2200' above sea level. My car had 28mm vents and drove like a bus, lots of torque no top end. Dellortos require a little bigger idle jet than Webers.

What is your weather like out there? If it is hot use a 65 idle and work down from that. Also what linkage are you using? If it is that shitty CB crossbar garbage get rid of it. Order a Bugpack center pull syle linkage.

It will not work right out of the box. You will have to modify it yourself. You want it as close to the center of the case as possible. Grind the legs off and shape it so it sits in the notch beside the middle bolt on top of the block. After you get done with that weld two washers on the top and bottom of the bell crank. Carefully file the washers to a perfect fit. There must be minimal slop and minimal drag as that piece turns. Put a long bolt through it and fit a lock nut on the underside of the pivot stand.

Then you will have to build custom arms. Use all thread to connect to the throttle balls to the center pull. You will want some adjustment. You will also want to make sure you have some adjustment in the linkage pivot points. Then you get the joy of spending a long time getting things just right. Making sure the carbs open at the same time and same rate.

This is the only way you can get your car just right. I ran 36 chokes in a 2056 and had no problems. It ran a little fat but that is the best way to tune it out unless you GO FI.

You may also try to bring the timing in sooner and maybe bring a little more.

brett,

humm... i am already running 12 deg initial timing, and 29 degrees in by 2900 (grey grey mallory springs)

bump up the initial? and fatter idle jets.....

Aaron, I have a question regarding this hesitation. Is this a foot to the floor, wot, from idle or is it a slow application of throttle? The first would indicate accelerator pump the second would indicate progression system, idle jets or linkage. I've been playing with my 40's on my 1.8L. One of the things that I've been doing is balancing the carbs at idle and then balancing them again using the linkage at around 2500 rpm. I pull the throttle cable housing out a little and place a little spacer to hold it in place (about 1/8"). Then check the flow on each side and use the throttle linkage to balance them out. The adjustment should be minimal.

I don't have a lot of experience with jetting. I bought Tomlinson's book on your recomendation. It's my third book on Weber Carbs. The thing that I noticed is that they all vary some what on the recomended jetting.

For Weber 44, 2.0L:

Idle jet:
Tomlinson: 60
HP Books: 50

FWIW.

Bill

its from middle throttle.....

WOT it gets there...

bt from idle, and progressively increasing pedal, it gets to the top of idle circuit nicely, tehn gets shitty, sputter, pop, bog.... give it WOT and it goes...

ill try the 55 idles....

Ok timing seems alright. Go up in idle jets. Also make sure all four idle jets are the same. Don't take it for granted.

Also make damn sure your linkage is working freely and within the proper range. Make sure your carbs are opening at the same time and rate.

Aaron, yes 55 idles. will get you better running. I finallt decided to buy a set of jet reamers and gauge. I am satisfied with what I estimate as 53 idles. 55 was a bit rich and 50 was way too lean and caused the exact symptom as you have.
Also if you remember back loast month I replaced all my intake gaskets with new ones. You wouldn't think they leaked but yup ever so slightly. Enough to cause that heistation you describe. (exactly what I had).

My 40 IDF have 32 vent. I usedto run 44's with a 38 vent I don't know how high it would rev but it pulled to 7 grand in 4th pretty quickly before I let off.
The 40's run out around 6500.

ok.. so i started beating the beast after work today....

brando droped by and helped.
So.. we changed out intake manifold gaskets. GUESS WHAT. the old ones were the hard phenolic kind and were TOAST. literally crumbled!!!! one had a big crack

"Hey aaron, i bet you had an airleak!" LOL

so we did that. then, i pulled idle jets and swapped in the 55's, blew out all the passages with carb cleaner and buttoned it up.

havent touched any idle mixture screws or airbleed screws at all... just drove it.

the transition stumble is GONE. its a little fat down low... but i havent touched mixture screws yet, and... most importantly it still has some bottom end.

so we went for a spirited test drive.....

did a nice launch, and blowing by people with the short gears on the 1tr mile on ramp.....

get to the end, hit 5th... and its on 3 cylinders LOL..... uh.... bummer man.

pulled over on the freeway... and a spark plug wire had been knocked loose in our manifold gasket changing excercise... and musta been barely on....

back on all 4... ready for some syncing and mixture settings and then I AM DONE

thanks for all the input guys!

AA

Ready for a road trip or fun run?

At least after the weather cools down...

im gonna start syncing and tuning em tomorrow between school and work...

soon. i am ready

My money's still on skline for finishing first. AA will just find another little thing and tear the whole car down again. Dirk Wright lives!

howard. i spend too much time here instead of working. (and working on kaptkaos' car )

i think skline found love and wont finish the car.

now.. onto hunting electrical gremlins... and then redoing dash face, and adding GT panels, finishing GT lid, Oil Cooler Ducting... etc...

when can i expect your help? bring the stoli

Whoo Hoo! what do I win?
Wanna bet you end up going back to the idle jets you had in there in th 1st place?

Only cuz I been there done that 2 weeks ago.

watch... i have to ream up to a 53 LOL.......

RRC or BUST!

ABout the only way to tune to that level specific level is with an A/F meter.
then it is all about air density, Temp, humidity.
Works great for 80 degrees but not worth diddly at 100 degrees.

hah... wonder how many altitude and temp changes will occur on my to utah LOL....

[quote name='Aaron Cox' date='Jul 22 2006, 05:13 PM' post='735105']
today, car felt shitty. it was backfiring etc... hasnt done that in a while. i am gonna change intake manifold gaskets, and see if i have an airleak...
===================
Can anyone tell me what causes the Weber backfire. I have 4 on an Ingelese on a 350 SBC which was running pretty reasonable. To get it tiptop, I had a guy rebuilt and setup all 4 and now I get severe backfire when decelerating. Not the timing, I checked, plus these were initially set up for the engine and there was no backfire just before the Webers were rebuilt and "readjusted".

WAY lean.
I guess the progression of lean is:
2. runs hot
3. stumble off idle but zooms away (intake gaskets)
4. Stumble with bucking on acceleration (idle and acceleration jets)
5. backfire through carbs on any of the circuits
6. bucking / surging upper RPM range (main jets)
7. Whhaaaaaaa BANG too lean from no gas

*UPDATE*

ok... so it is 105 out right now. i braved thru the heat....

closed all the air bleeds as per your suggestions (vs tomlinson book), every barrel flows ALMOST the same full closed....

Started with mixture screws 3 turns out.... ened up, 2.25 turns out with the 55's....

played with idle speed screws just a tad.

and now the BITCH IS MOVIN! it scoots...

so i am 99 percent done... maybe i will put the 50's back in and end up 4 turns out or so... but damn... car launches and flies when it comes on the cam......

i am a happy camper.

dank joo berry much!

That would make no sense. 4 turns out wiould indicate the jets are too big. You just said it scoots with the 50's and runs great.

wrongo

with the 55's i am 2.225 turns OUT. (leaner)
if i put the 50's in i would need to be richer (maybe 4 turns out)

runs fine right now. if it is too fat down low, i will try the 50's as i mentioned

turning out is RICHER and turning in is LEANER

Screwed that up completely didn't I. Gotta quit postin while I'm trying to work.

Still though, 4 turns is too much the other way (rich then LOL). I'd seriously look at reaming a set of 50's. or leave it the way it is now. A little fat at idle won't kill ya.

two things ...

1. 44's for a 2.0L is way too big. go with a set of 40's instead ...

2. if you don't like 1., go down on the venturi size. i went down to 32 on my warmed over 2056 and it got rid of all the "flatspot" and hesitation at half-gas ...


oh, and i HATE carbs ...
Andy

I guess the only thing else I have to say is some people seem to be hung up on how many turns of the IDLE mixture screws is good or bad.

Yes there is some truth to 4 being too many indicating need bigger jet.
But that is only IDLE and a few RPM's past. after 1500 RPM the idle mixture screws have shut off and the progression ports have kicked in. You are now on total idle jet. here is where a Meter will tell you where you are at.
The idle jets don't start weening down till over 3000 RPM. where the main jets take over. So, OK that's how I see life with carbs.

I think that the F16 emulsion tubes are a big help fo smoothing the transition on Weber carbs on Porsche engines. Our expierence with 4s and 6s is that they do not like a lot of fuel too soon. I have carbs on 6s, both Webers and PMOs and we went to F16 emuls on the PMOs and F24 on the Webers to get a smooth transition. If the idle screws are more than 2 turns out, you need to go up one step (ie. 50 to 55).

Or like Aaron and I have done. Get better ignition. 50,000 volts will light alot of gas.

60,000 volts here joe LOL

ask clayton. he saw my arm get zapped when i fubard the test procedure for the box LOL

i like it where it is right now...

andy, it is choked down pretty good with the 34's...

arent 40's with the 34 vents the same as 44's with 34 vents?
i guess i can see where right after the venturi, where it goes back to full diameter where the progression ports are..... might slow down air speed.....

seems to work ok here....