webers working themselves out of tune...are mine the only ones? - Alfa Romeo Bulletin Board & Forums

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Old 05-03-2012, 04:11 PM
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webers working themselves out of tune...are mine the only ones?

My webers seem to work themselves out of tune, idle circuit, fairly regularly. Is this something common?

It seems at least once a week I find myself in the engine bay tweaking the idle mixture screws to fix my air fuel ratio at idle. After a few minutes they are dialed back in and driving bliss.

Just to give you an idea I dialed them in on Saturday. Drove her home from the shop. Parked it till Tuesday. Drove her Tuesday and Wednesday, maybe 10-15 miles. Some soft some hard. When I parked her last night she was way out, sputtering, poping, and stalling. Warmed her up after work today, with at least one annoying stall out. Tuned her up and perfect idle and smooth running.

For what its worth they are mounted onto a recently rebuilt TS that was balanced when rebuilt. I have also had a couple small parts vibrate off them.

Thanks for the help.
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Old 05-03-2012, 04:18 PM
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Your experience is not normal. Mine go years without adjustment. Maybe you have an air leak or maybe the butterflies are not closing consistently. Hopefully Gordon Raymond will read this and give you some advice.
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Old 05-03-2012, 04:45 PM
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Do you have a support to the outside of the Webers to the engine mount on that side? Are you using a "converted" FI manifold with "O" rings in place of the insulators / isolators? Have you checked the screws position; are the springs weak enough that they can move? Any of the above will cause this problem, you may be just a little bit lean on the idle jets, maybe one step.
Engines in a fairly high state of tune sometimes do this with temperature. My GTA engine likes a little change above 80 degrees, and again at about 55 degrees, but it is not a street engine. Constant Weber adjustment usually indicates something else is wrong, from air leaks, bad fuel, incorrect jetting, and so on. It can be plugs, wires, distributor, a weak coil, valve clearances as it will affect cam timing and so on. Most often not the Webers. You adjustments are a band aid for another issue.
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Old 05-03-2012, 04:59 PM
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Thank you both.

I am not currently running a support strut. It will require a different setup to get one mounted. Will have to put that on the list.

I am using the Alfaholics intake manifold with the double o-ring thin plastic isolators and spring washers. I have to admit I am running the spring washers fairly well compressed, more than recommended by instructions.

I have had air leaks in the past so I am not ruling them out but when I remounted the webers on Saturday after changing the throttle linkage setup I spent some time with the brake cleaner can checking for leaks; I did not find any. I will have to check again.

They did not unbalance for what its worth. When I checked them today with the syncometer they were all spot on at 3.5 whatever units.

These are bran new carbs I would be surprised if the springs were weak. I was actually thinking of marking them with a sharpie and see where they go next time they go out of tune.

I will report back with a little video if I get a chance tonight. Thanks again guys. Headed out for a drive!
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Old 05-03-2012, 07:33 PM
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What is the full model number of your Webers and what idle jets are in them? About how many turns from full closed are the idle screws?
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Old 05-03-2012, 08:46 PM
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If you disable the function of the O-ring / spring vibration damper by over tightening them AND donīt have some support (also with some rubber in it, like the stock item) to take the weight of the carbs, you will sure run into trouble. Please take this serious!
I understand you made the springs tighter than advised, because you wanted to compensate for the missing support. but that is wrong.
But even so, a new set of Webers does not work its idle screws loose.
The popping and stalling you describe seems to have its cause in a weak mixture, so I would look at the fuel supply first. Maybe you have too much fuel pressure leading to a high fuel level at idle. So you adjust the idle screws in a lean position to compensate. When you have load on the engine, fuel level returns to normal, making your idle jet give a lean, normal mixture. So strong vibration at the carbs and a too lean idle jet are a possible cause. The idle can be adjusted with any idle jet, but transition and low load suffer.
Even the ignition can be responsible, as a weak or late spark may not be able to ignite a leaner mixture, that otherwise would still burn. Defects on ignition parts often show up after some time of heating the engine bay and disappear with cold components or even an open hood.
I don`t know your set up, but donīt run high tension cables and sensor wires in parallel or close together. May look neat but produce unpredictable problems.

As always, long distance diagnostic is not precise and may miss simple causes because of second hand information and subjective impressions.

Good luck!
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Old 05-04-2012, 07:38 AM
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Here is a link to a video of the engine idling. There is a little vibration, its not a v-6 or 12 after all, but its not terribly bad. your thoughts.

Quote:
Originally Posted by AlfistaChris View Post
If you disable the function of the O-ring / spring vibration damper by over tightening them AND donīt have some support (also with some rubber in it, like the stock item) to take the weight of the carbs, you will sure run into trouble. Please take this serious!
Yeah this is exactly what I have done Need to add the support bracket asap and then loosen up the nuts holding on the webers. The Pipercross filter backplane is not ridged enough for a strut mount so I will need to machine something appropriate.

Does anyone have a cad drawing of this plate?

Quote:
Originally Posted by AlfistaChris View Post
Maybe you have too much fuel pressure leading to a high fuel level at idle.
I am using one of those fancy glass filter regulators set to 3 psi. You can see the regulator/filter in the lower right in the picture below. I just recently pulled the inline pressure gauge off. For the last month that the gauge has been there the pressure never went out of wack, no reason to think it did since Saturday.

Quote:
Originally Posted by AlfistaChris View Post
I don`t know your set up, but donīt run high tension cables and sensor wires in parallel or close together. May look neat but produce unpredictable problems.
Not the latest picture but shows the engine bay's configuration. All my signal wires run along the fire wall to the passenger side fender and then underneath the air filter. For a short length the (3" maybe) the battery cable passes by the signal wires and then for another short length (10" or so) the alternator cable also runs parallel to the signal wires. The spark wires only run 90* to the signal wires. That should be okay, no?



Quote:
Originally Posted by AlfistaChris View Post
As always, long distance diagnostic is not precise and may miss simple causes because of second hand information and subjective impressions.

Good luck!
Roger that but I'll take what I can get Big thanks everyone.
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Last edited by Seabird; 05-04-2012 at 07:40 AM. Reason: added video link
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Old 05-04-2012, 08:39 AM
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You will find the pressure regulator is there to help damp fuel pulses from most fuel pumps, as well as pressure regulation. The exception is the very expensive radial vaned aircraft fuel pump. This delivers no pulses, and the vanes are engineered to fold to drop pressure at specific PSI. More than 3 PSI running will overwhelm some needle and seat sizes yielding rich mixtures across the normal operating range. More critical is the fuel pulse hammering effect that will tap divots into the Weber float paddles reasonably quickly. This causes float levels to change, and in extreme cases, the floats to stick. The cure is new floats. Below is a picture of a float paddle divot. This one is still workable, but not ideal.
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Old 05-04-2012, 06:30 PM
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Your car looks very nice. Good work.

The combination of 3 psi, which is at the high side for a Weber, and the vibrations may cause your problem. You could reduce the pressure to something like 1 psi and get the vibration damper to specs.

You seem to have a special ignition system. I do not know which one, but the problems can come from that side too. If the carb stuff does not help, try to put the ignition in a basic mode so nothing unexpected can happen with these settings.

Did you have someone who did the combination of parts for your engine?
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Old 05-08-2012, 05:52 PM
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Finally got the car back over to the shop to correct my ignorance Tweaked, balanced, tuned, balanced, and was back on the road. I drover her home and she kept her idle adjustment. So instead of pulling in I went for a 20 min drive.

I mixed it up between cruising and hard acceleration to see if anything would shake out. All was good. Idle circuit stayed in tune, I was very happy to see this.

Air/Fuel as displayed on my A/F gauge was a little all over the place while at varied loads and rpms. Nothing to out of the normal range but not really what I expect.

Gordon pointed out that Centerline offers the beefed up carb support plate and strut so I will be ordering this tomorrow. I might have to adjust the strut length but this is easier than fabbing up the whole thing.

Thanks everyone for your help I will post a pic once its all corrected.

Regards,
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Old 05-11-2012, 01:24 PM
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Quote:
Originally Posted by Seabird View Post
Air/Fuel as displayed on my A/F gauge was a little all over the place while at varied loads and rpms. Nothing to out of the normal range but not really what I expect.
Obviously I don't know how far your A/F mixture is varying, but I would say that with carbs, a lot of variation is normal. Carbs just don't meter fuel that accurately. When you open the butterflies, the accelerating pumps will produce an over rich mixture. With the butterflies closed producing high vacuum, it will be under rich.
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Old 05-11-2012, 03:49 PM
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I have an A/F meter in my Spider which has Webers. The meter shows how Weber setup is such a compromise. For me the main thing is that the mixture is in the right range at WOT at medium to high rpm. It is not a concern to me if I am running lean a part throttle as it is doing no damage and is saving a little gas.
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Old 05-21-2012, 01:44 PM
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Okay so the Centerline support plate does not line up with the TS head, should have known that, well kind of did, still went down that road, now I am out on the other side.

Going to be producing one on a CNC specific to the TS. I have a post dedicated to this over here >>> TS Carb Support Plate Thread

Enjoy!
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Old 05-23-2012, 05:41 PM
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Okay so the plate and strut might be the best addition to the car that I have made second only to driving it to seat the rings, but that's another story. Seriously the strut is magic!

Yesterday I mounted the plate and took her around for a spin. The usual pops and sputters that have been a regular part of my driving experience. The carbs did not work themselves out of tune but it was not a long drive either.

Today after successfully modifying the Cenerline strut and installing it the car was a dream. No back fires, no attempts at stalling out, just smooth idling and running.

Thanks everyone for your valuable input.
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