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Weber Recipe?


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Hi Peter,

So the last i to dot is the float level - if too low the main system won't come in at low enough rpm. 

Yes, the 4 degrees ATDC was only meant to be operative at idle on emissions engines. Once the throttle starts to open a valve operated by the linkage dumps the retard capsule and static time takes over, then centrifugal and vacuum advance raise it further. With the original distributor ~ 50 degrees advance is possible with 10 degrees static time.

Tom

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At last!!!

I have been trying to get sense out of these Carbs for weeks now and now I've set the timing correctly, it all falls into place :)

Thanks Guys for all your help and suggestions, I am now really pleased with the results.

Next stop rolling road for a measure up, will keep you posted.

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5 hours ago, unclepete said:

At last!!!

I have been trying to get sense out of these Carbs for weeks now and now I've set the timing correctly, it all falls into place :)

Thanks Guys for all your help and suggestions, I am now really pleased with the results.

Next stop rolling road for a measure up, will keep you posted.

Clad you got it sorted,however the advance curve on the dizzy will be out for a CP cam but the hp difference will not be that bad.If you want to get the best out of it suggest you get this sorted before RR if you have a good operator that knows what they are doing.  

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Which cam did you finally use? 

You originally stated it was a standard CC engine with 2500S head (307621 cam) then it is CP and you gave the timing of 307689 cam.  The CP cam is a wise choice compared to the 307621  although the half way house would have been the 311399 CR and CF cam.

PDF of 6 cyl cams courtesy of Chris Witor

https://www.chriswitor.com/cw_technical/camshaft_applications.pdf

Are you sticking with the vacuum advance and retard setup for driving economy purposes ( advance) and tickover emission (retard)  There is a replacing adjuster item for the advance vacuum capsule (517426)  item 20 here (£71.00!!!)  That would make the double capsule distributor look more like a CP item I suspect.  https://www.moss-europe.co.uk/shop-by-model/triumph/tr5-6/electrical-system/ignition-system/ignition-system-distributors-tr5-6-1967-76.html

 

Cheers

Peter W

 

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4 hours ago, BlueTR3A-5EKT said:

You originally stated it was a standard CC engine with 2500S head

My Fault - I double checked the cast and stamped serial numbers and it is a CR Head on a CC Bottom End.

 

4 hours ago, BlueTR3A-5EKT said:

Are you sticking with the vacuum advance and retard setup for driving economy purposes

No - There are no vacuum take offs on the Webers so I have ditched the Vacuum Advance.

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Peter,

You don't need vacuum advance for the CP setup; after all TRIUMPH didn't employ one on those engines. If you have a 13 degree distributor ( emissions standard fitment ) I would set it to 4-6 degrees BTDC static; that's how I ran mine for tens of thousands of miles before switching to a 7 degree distributor set to 10-12 BTDC. Performance pretty much the same; no noticeable difference. 

FWIW, I use NGK BP7ES plugs gapped to 0.030".

 

Tom 

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  • 1 year later...
On 5/10/2022 at 1:54 PM, unclepete said:

Hi Tom

Have gone to electronic ignition - just a whim - and can't check the static timing...

Have you got your ignition setting at idle?

Hi Pete,

If you want the best out of your Webbers? Go and find your local Ford or Lotus Club they will know a local person who can tune your carbs to a state that you would be lucky to achieve plus no aggro and cut out all the farting about!

Bruce.

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On 12/1/2020 at 7:26 PM, BlueTR3A-5EKT said:

Which cam did you finally use? 

You originally stated it was a standard CC engine with 2500S head (307621 cam) then it is CP and you gave the timing of 307689 cam.  The CP cam is a wise choice compared to the 307621  although the half way house would have been the 311399 CR and CF cam.

PDF of 6 cyl cams courtesy of Chris Witor

https://www.chriswitor.com/cw_technical/camshaft_applications.pdf

Are you sticking with the vacuum advance and retard setup for driving economy purposes ( advance) and tickover emission (retard)  There is a replacing adjuster item for the advance vacuum capsule (517426)  item 20 here (£71.00!!!)  That would make the double capsule distributor look more like a CP item I suspect.  https://www.moss-europe.co.uk/shop-by-model/triumph/tr5-6/electrical-system/ignition-system/ignition-system-distributors-tr5-6-1967-76.html

 

Cheers

Peter W

 

To get the best out of Triple Webbers you need something in the way of a cam shaft that is a lot better than 307689 like a Newman PH2 or if you can find one a BL S2  ( BL special tuning part)which was sold in the USA or a SAH 357 ( based upon a S2) these cams were designed for Lucas PI or Triple Webbers with 10 to 1 compression. The other cams that you quote are a lot of money spent on carbs with not a not much more go???

Bruce.

Bruce.

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  • 11 months later...

I know it's been nearly a year since my last post on this subject but I hope some of you guru's out there will have an answer..?

The engine all runs fine except it gets a little bit buried when accelerating from tickover which is a pain in traffic!

Where on the Carbs do you connect the vacuum pipe from the dizzy? I have heard you can fit a barbed fitting in one of the air bypass screw holes?

Edited by unclepete
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Never had vacuum pipes on any of mine Pete, in fact when Martin built my last dizzy he blanked off the hole. You sure it's not just a case of tweaking mixture screws or altering the idle jets to improve the transition from the idle circuit to the mains?

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2 hours ago, Chilliman said:

 You sure it's not just a case of tweaking mixture screws or altering the idle jets to improve the transition from the idle circuit to the mains?

Thats more like it.

Stuart.

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9 hours ago, unclepete said:

The engine all runs fine except it gets a little bit buried when accelerating from tickover which is a pain in traffic!

If I understand your parle..  my 4A SU carbs seemed balanced but the engine suffered spluttering at bottom end pick up.  Pulling away from junctions or from tight corners was horrid.  I sorted that by very accurately synchronizing the link rods, so each carb started to pick up at exactly the same moment.  Your Webers wouldn't have the same rod linkage but still each carb and each choke must start to open at the same time and by the same amount.

Hope that helps, Pete

 

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On 4/17/2023 at 3:11 PM, Chilliman said:

Never had vacuum pipes on any of mine Pete, in fact when Martin built my last dizzy he blanked off the hole. You sure it's not just a case of tweaking mixture screws or altering the idle jets to improve the transition from the idle circuit to the mains?

 

On 4/17/2023 at 11:58 PM, Bfg said:

If I understand your parle..  my 4A SU carbs seemed balanced but the engine suffered spluttering at bottom end pick up.  Pulling away from junctions or from tight corners was horrid.  I sorted that by very accurately synchronizing the link rods, so each carb started to pick up at exactly the same moment.  Your Webers wouldn't have the same rod linkage but still each carb and each choke must start to open at the same time and by the same amount.

My Dizzy is going off to the Doctor!

To quote Martin "You  can't  satisfactorily  connect  vacuum advance  with  Webers, so  you  need to optimise the  centrifugal  advance to  compensate  for that  &  the  mods that  have  been done"

Watch this space.....

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The off idle stumble issue is probably the hardest to sort on webers. I think mainly because there are a lot of parameters that are combining. A crucial part is getting the carb setup so the transition circuit holes are uncovered by the throttle plate at the right time and in synchrony across all throats. As the position of the throttle plate before transition is influenced by the idle mixture, timing, choke size, emulsion tubes etc you can see the issues. Keith Frank at side draft central is probably the king at this and ahs developed a number of new emulsion tubes and jets that help. 

Tim

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8 hours ago, unclepete said:

My Dizzy is going off to the Doctor!

Good choice Pete, at least you'll be able to rule that out of the equation. Tim makes some valid points about the stumble from idle to mains. In all my years of running Webers it has always been one of the most challenging aspects. Webers are wonderful carbs & there are hundreds of tuning combinations available to get them precise for your own engine and needs but by the same token there are also hundreds of ways to get them wrong!

I've probably read every authoritative document you can imagine on Webers (even understood some of them!) & I'm still learning.

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I have a 205 Rallye with twin weber dcom 40's, but these carbs do have an accelerator pump on both, but have suffered the stumble for ages and ages, but have now found that the idle jets that were advised in the original manual are far too small, ( perhaps the fuel is different now) and have fitted some much larger idle jets, and have reset the butterflies with an air flow meter, and it has at last transformed this pocket rocket,  105 hp standard on 1295 cc !!  Its just a matter of keeping it on the road!

I thought that there was a jet listing for these engines, can you tell us which ones you have in at the moment?

John

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Pete when you get the car running again if not happy i use a local rolling road who have sorted 3 full race 6cyl engine cars with webers.

Always feel hesitant to recommend companies but if you want to give them a try PM me and i will forward their details to you.

Roy

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There is no mystery to setting up Weber’s use search for those that have been using them for years and rolling roads are not the be all they are cracked up to be and setting up for road use and race cars are totally different 

dame I said to myself don’t post anymore 

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Hi Neil,

Nice to see you on the forum again.

regards Mick Richards

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