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Triple Webers running rich and spitting back at lowish revs


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As it is easy to do, I suggest plumbing the depth of the fuel in each carburetor after priming. Take out a main jet stack and drop a gauge rod of your own choosing into the well. The depth should be the same for all (3). For reference, mine are all at 28mm below the top of the well.

 

Tom

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Tom - if they not at that level what do I do?

8 minutes ago, Tom Fremont said:

As it is easy to do, I suggest plumbing the depth of the fuel in each carburetor after priming. Take out a main jet stack and drop a gauge rod of your own choosing into the well. The depth should be the same for all (3). For reference, mine are all at 28mm below the top of the well.

 

Tom

Tom, if they are not what you say what should I do??

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If they are not equal, either the needle valve is not sealing or the float isn't set right. Report the values of the (3) carbs and we can steer you toward getting them sorted. Brass and plastic floats have different settings, 12-14mm for plastic and 5-8.5 for brass are the typical range in this application, both yielding fuel depth measurement from 25-28mm below the well top.

This is not a common issue; it's just due diligence since you're having a problem.

 

Tom

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2 hours ago, John L said:

Thanks for sharing that, John. 

I bought a Plexiglass gauge from Keith years ago and appreciate his devotion to Weber DCOEs. His experience is mainly with LOTUS engines and I was surprised he's only tuned with (1) emulsion tube - the F11. There is a great deal of difference between these and his advice would be worth much more with this aboard. Having tuned a few TR250/6 engines ( mostly my own under differing build recipes ) I prefer the F2 and F7 emulsion tubes as they seem to bring the main system into play at lower rpm - especially the F7 which both my engines now use. FWIW, F11s are not as generous at lower rpm, nor are F15s and least of all were F16s in my experience. 

He also advises setting the floats/ fuel level to 25mm below the top of the well. WEBER had different values for different applications and in fact set it lower in the LOTUS applications. The " generic " setting in published literature works out to 27-28mm. 

The main thing I got out of this paper is his suggestion that idle - to - main jet system transition should be around 1400 rpm. I was thinking 1500 is the low end of where reasonable people would expect to get any response from WOT. First time I've come across a suggested rpm for it.

I believe that cruising at 3000 rpm or less uses only the idle circuit, vacuum scarcely felt beyond the throttle plates. He says otherwise, so those more in the know can chime in.

Maybe I"m lucky but rocky idles have not been an issue for mine - but they're 6-cylinder ^_^.

 

Tom

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If fuel bowl height is correct next step is to check idle setscrews and progression holes.

Backfire of 5&6 while 1-4 is rich indicates that there is something severly wrong,

not only setting the idle screws but systematic because backfire means lean mixture.

Backfire when opening throttle a little bit is indicated to idle system and misfire at large

opening is related to main system including venturi and mixer behind. That must be bolted

properly and oriented correctly to be pressed upwards.

Edited by TriumphV8
missing idea
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3 hours ago, TriumphV8 said:

If fuel bowl height is correct next step is to check idle setscrews and progression holes.

Backfire of 5&6 while 1-4 is rich indicates that there is something severly wrong,

not only setting the idle screws but systematic because backfire means lean mixture.

Backfire when opening throttle a little bit is indicated to idle system and misfire at large

opening is related to main system including venturi and mixer behind. That must be bolted

properly and oriented correctly to be pressed upwards.

My view is that triple Webers DCOE type can only be set up properly on a rolling road with an AFR stuck up the exhaust. Now the hard part is finding someone who still has the skill to set them up with that type of facility. Otherwise you will  end up cursing and swearing. Having had a car with 2 DCOEs I know the problem well!

Bruce. 

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45 minutes ago, astontr6 said:

My view is that triple Webers DCOE type can only be set up properly on a rolling road with an AFR stuck up the exhaust. Now the hard part is finding someone who still has the skill to set them up with that type of facility. Otherwise you will  end up cursing and swearing. Having had a car with 2 DCOEs I know the problem well!

Bruce. 

I know a guy called Tom Airey who's a wizard on tuning carbs including Weber's and has a rolling road. He's based in Hampshire. 

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On 6/20/2020 at 1:25 PM, astontr6 said:

My view is that triple Webers DCOE type can only be set up properly on a rolling road with an AFR stuck up the exhaust. Now the hard part is finding someone who still has the skill to set them up with that type of facility. Otherwise you will  end up cursing and swearing. Having had a car with 2 DCOEs I know the problem well!

Bruce. 

For this problem it will be the wrong way!

Rolling road or AFR measurement always takes all 6 carbs into account.

AFR for example if made rich by the first four carbs and leaned by the two in the rear,

will give a wrong intermediate figure.

 

So the result is not suitable for any decision and also power measurement will end with

the best performance the engine will give under these circumstances and not under proper

setting of all six carbs,

 

Before any testing is done you must be sure all six carbs are performing same way.

 

Unfortunately the rolling road will not cover the way we will drive under part throttle. The limit how lean we can go with the setup is indicated by several things, mainly the cam will need a richer mixture if hotter. So it is an individual driving test necessary to find the proper idle jets that meet the drivers preference and save fuel as good as possible.

 

If not needed I would set the carbs to 13AFR over the whole range and a little bit richer at full load.

It will take some more fuel but the setup is quickly done.

 

I would not expect some more performance on a rolling road from a TR6 set by me on the street compared

to the rolling road because we know the ignition advance very well. Although I do not know the absolute number

in BHP the setting on the street is perfect if you know what you are doing.

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  • 2 weeks later...
On 6/22/2020 at 6:49 AM, TriumphV8 said:

 

I would not expect some more performance on a rolling road from a TR6 set by me on the street compared

to the rolling road because we know the ignition advance very well. Although I do not know the absolute number

in BHP the setting on the street is perfect if you know what you are doing.

Apart from a brief fling with a Lumenition A/F ratio meter ( which told me nothing I didn't guess anyway, before it quit working altogether ) it's been seat of the pants and monitoring fuel economy for mine, 142K miles total over 24 years. Could be that more tweaking would bear fruit but I reckon only a token amount, if any.

But we don't have competent rolling roads with Weber expertise on every street corner here in the 'States like you have on your side of the pond ^_^.

 

Tom

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