Weber Idle Air Bleed adjustment opinions

[keitho64]

Question for you Weber gurus. I have read many threads on webers. Some say to adjust the idle air adjustment with the engine at idle to get equal vacuum through each barrel. I have also read where it says to do this with the engine at 3,000.

According to PMO's documentation they say to set the idle air bleeds closed to start and then adjust last for equal pull through the throat. It also says the air bleeds help to lean out the idle circuit but do not effect the transition.

My car is a 2.2S, 32mm venturis, 55 idle, 130 main, 180 Air corrector, f1 tubes. For the past year it has always had a problem between 2,000-3,000 in a steady cruise and then gentle acceleration. When you gently hit the pedal the car will pop through the carbs and then go. If you mash the pedal it would take off. Well now it is much worse and the performance is suffering so I plan to readjust the carbs but thought I would poll the experts for some advice.

What experiences have you had? How do you set the idle air bleed adjustments?

[jwetering]

I'm far from an expert, but I always set mine at idle, which I always believed was the procedure. This is the first time I've heard of adjusting them at 3000 rpm. Seems to me my air flow meter woudl be prety much pegged with the car pulling 3000 rpm, making it impossible to get a good read or to adjust.

[RoninLB]

you may get different readings if the cross linkage is not adjusted to show equal openings.

[2.7RACER]

Keith,
I just happen to have my webers off my motor today.
I took a number of photo's for my own use.
Upon inspection the idle circuit becomes quite simple.
This picture looking into the base of one barrel shows the small port below the butterfly valve and also the slot and hole in the base of the carb.
When the engine is in the idle mode, the butterfly is closed, blocking fuel and air from the intake of the engine.
The small port shown below the butterfly is where fuel enters the intake. The amount of fuel is controlled by the idle mixture needle valve.
The fuel flows from the float bowl through the main jet, then up through the emulsion tube, then through the small idle jet, then down to the idle mixture port. The idle mixture screw controls the amount of fuel that flows through the small port below the butterfly.
At idle this is the only fuel path to the intake when the butterfly valve is fully closed.
At idle air flows through a small port above the butterfly down to the air screw needle, then to the port in the picture.
Except for any air leaking past the butterfly valve this is the air path for idle.
Once the butterfly valve is opened, even slightly, fuel flows through ports above the butterfly valve and of course air flows past the slightly open butterfly.
As you can see from the second and third picture these ports are open to the intake once the butterfly opens.
The third picture is from the outside with the brass cover removed, the air screw is to the right, the fuel screw is below.
So you can see it is appropriate to adjust these two screws in the idle position.
If PMO says these screws are adjusted at idle, I would follow their instruction.

[davidppp]

An excellent analysis indeed.

The confusion arises because most sources advise the idle mixture screw, (Not the idle air blled screw) be adjusted at about 2 000 rpm.

The function of the bleed screws is to bring the air flow throught the 5 chokes with the less leaky butterflies up to the flow of the leakiest one, with all the linkages disconnected and the throttle stop screw backed out to close everything fully.

The bleed screw on at least one choke will therefore be fully shut when correctly set..

Kind regards
David

[2.7RACER]

David,
The only reason one idle air bleed screw would end up completely closed is if the butterfly valve is not properly set up.
There is a procedure to adjust the butterflys' so that each is properly closed at idle.
To synchronize each throat to one throat not fully closed or leaky would in my estimation attempt to set the carbs to a higher air and fuel flow which will result in a idle speed higher than designed. Not really a true idle.
Better to address the issue of the leaky butterfly valve.

[davidppp]

Hello, Doug.

Of course you are correct, but in practice it is impossible to ensure all butterflies seal well..and there is usually some air via the throttle spindle.

Weber knew this and provided the idel bleed valve for this very purpose..

Kind regards
David

[RoninLB]

Originally posted by keitho64
Question for you Weber gurus.

My car is a 2.2S, 32mm venturis, 55 idle, 130 main, 180 Air corrector, f1 tubes.

problem between 2,000-3,000 in a steady cruise

and then gentle acceleration. When you gently hit the pedal the car will pop through the carbs and then go. If you mash the pedal it would take off.

I have no experience with webers so only guessing here. I assume the carb parts are correct for the application as different idle jet holders affect the mix, etc. I also assume the basic adjustments of floats, idle air, linkage, etc are correct

Steady cruise up to around 3k+ish is idle jet operation. You may have to run 3.3k in 5th gear with the S cams? I'd set the idle AF mix screws all Equally and as lean as possible to allow nice steady operation in 4th & 5th gear.
ie: if the 3-3.3k steady cruise is nice at 2.5 turns try 2.25 turns on all. If it's popping it's too lean at that steady running setting. Then you know that 2.5 is your adjustment. A .25 turn is significant imo.

The acceleration circuit flow should also be set as lean as possible imo.. [after the idle mix is steady when cruising]. Slowly lean the acceleration flow till it develops the leaning and popping then slowly increase till it stops. I start this without driving. I'll test by bringing rpms up to a steady 3k, 3.5k, 4k, then whack the throttle gently then more so to see if its reached the lean popping. Once it's above the lean condition I know that when driving it'll be lean at this point so I'll slightly richen the flow from that non-driving point.

I'd do all this with clean hot spark plugs.

I think once you establish a baseline you'll be able to easily correct the Weber transistion problem which may mean opening the idle AF mix screws ?

[keitho64]

Thanks for all the excellent replies. I am going to head into the garage tonight and mess with the adjustments. I will post the results when completed.

[lateapex911]

One other thought....make sure you aren't having issues related to throttle shaft wear. it would, I think, be more widespread than your specif situation, it's just a consideration.

[2.7RACER]

Keith,
More thoughts on your problem. My first response focused on idle settings. However rereading your post it seems the reason for all this is a lean spot between 2000 & 3000 rpms.
At 2k to 3K, your motor is still running basically with fuel supplied by the three low range ports (my term) as seen in the picture.
So you have these ports plus what fuel flows thru the idle mixture needle valve supplying your motor at these rpms.
Now if you follow the fuel flow path, see next picture.

You can see all the fuel flows through the idle jet, in your case a 055 idle jet.
My thinking here is one or more of these jets are not completely open.
This is very easy to check. Pull each of the idle jets and check with a strong light. Clean as necessary.
I would also remove the brass cover screw just above the idle mixture screw and make sure the three low range ports are clear.
This can be done with the carbs on the motor. You might need a mirror and strong light to get a good look.
If all of the idle jets are clear, then I would consider going to a larger idle jet.
The symptoms you describe all point to a lean condition at these rpms. When you press the throttle hard and the accelerator pump squirts fuel, things work right.
So all you need is a little more fuel at these rpms.
Good luck and have fun,

[keitho64]

I went through all the adjustments and the car runs fairly good. I still have the stumble / stutter / spit in the 2,000 to 3,000 on minimal acceleration. I did have 60 idle jets in it last year but in a effort to lean it out to pass emissions test I went to 55's. Now that I have a clear understanding of the idle air bleeds I should be able to go back to 60 idle jets and try running the idle air bleeds out 1 - 1.5 turns to lean out the idle. I believe this will solve the 2-3,000 issue I have. As for now the car idles at 950, nice and steady, pulls to 7,000 easily and runs very strong. Tomorrow I will try the 60's and see how that goes.

Thanks again for all the advice.

[dvkk]

Keith, in your case the emissions test is your friend. The CO% while the car is on the dyno at low speed tells you exactly whether your idle jet is the right size. Post your numbers. If the 55 proved to be too lean, consider a 57.

I'm with David on the adjustment of the idle air bleed screws. Theoretically, one will always be shut. BTW, to everyone, do NOT torque them down tight. Let the locknut do the securing.

Are you using the squirl cage type syncrometer? If not, get one.

[2.7RACER]

Keith,
quote: "I did have 60 idle jets in it last year but in a effort to lean it out to pass emissions test I went to 55's."
It all makes sense now.

[keitho64]

I wouldn't mind trying a set of 57 idle jets. I have 52's, 55's and 60's but I have not seen 57's. Do you know where I can find them?

[keitho64]

OK I tried the 60 just to make sure. With the 60's the car is definitely to rich. I get a lot of popping in the exhaust. I also ran the car in the 2,000-3,000 range and the hesitation / popping on mild acceleration is still there. This time I ran the car at 4,500 steady and I have the same issue with the hesitation and popping on mild acceleration. If I hit it hard it just goes.

I put the 55's back in and this setup is by far the best. The car pulls to redline in all gears. At this time I think the main cause of the hesitation must be due to the throttle shafts. I guess it is time to send them in to get repaired.

I have read a few threads on Pelican and Bieker Engineering comes up as an excellent choice but I have read that their turn time is slower. Has anyone dealt with Van Hook Vintage Sports Car Services LLC? Anyone have other suggestions as to the best place to get the throttle shafts redone?

Thanks again for all your help.

Doug - Thanks for the great pictures, and I really got a lot out of your valve adjust procedure you wrote up. http://forums.pelicanparts.com/porsche-911-technical-forum/264722-valve-adjustment-post2641795.html#post2641795

[2.7RACER]

Keith,
You have to like a man whose automotive choices are all horizontally opposed.

[dvkk]

Have you verified the float levels are right?

[keitho64]

On the float level gauge I have there are two lines, a space of about 1/4" and then two more lines. I have the floats set about 25% of the way up from the bottom two lines. If I remember I will post a picture of what the gauge looks like. This is where I wish I had PMO's for the clear sight plug. I did check them with the car running at idle.