Weber Tuning help..., my webers need some love Options

[Aaron Cox]

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???

[J P Stein]

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 (IMG:style_emoticons/default/biggrin.gif)

[Aaron Cox]

ill put the 55's in....

and re tune....

mallory CDI and GIANT coil dont foul plugs (IMG:style_emoticons/default/smile.gif)

[Chogokin]

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!!

[Aaron Cox]

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

[Howard]

Have you thought about updating to FI? It's the latest rage. (IMG:style_emoticons/default/poke.gif)

[Chogokin]

I know my wife would kill me after dumping almost $1000 in these carbs if I didn't make them work, heh heh (IMG:style_emoticons/default/biggrin.gif)

[wertygrog]

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?

[Aaron Cox]

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)

[Howard]

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.

[Toast]

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.

[Aaron Cox]

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.

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...)

[Toast]

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. (IMG:style_emoticons/default/laugh.gif)

[Aaron Cox]

Doesnt changing venturi's dictate slightly less large jetting?

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

AA

[MarkV]

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.

[hmeeder]

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!)

[Toast]

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. (IMG:style_emoticons/default/confused24.gif) I just know from experience by changing the sizes until finding a good match.

[Aaron Cox]

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!)

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

[Flat VW]

Size does matter.

[MarkV]

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.