Weber settings

[mwhitaker]

Sorry- forgot to add in the above that I have 36mm chokes-brain fade strikes again.

Mark

[webbslinger]

I have to correct my previous post where I said I have 135 mains. That was incorrect, they are 130s. Also, I was going to mention that I set my float levels per Weber's instructions for 151s. The resultant fuel level is about 27.5 mm below the base. I know, I know, 25mm + or - .5 mm, but it works great at 27.5.

[jk952]

Another data point for you.
I have engine of 1700 cc about 10.5:1
chokes 32, main 130, air 200, idle 45f9, emul f16. Seems to work well, no stumbles or popping on overrun, maybe 125 main would be better but don’t have, (120 too small), with smaller air (160) seemed too rich but do not have a meter just checked plugs*, timing 10 deg. Std cams I think (no grooves ), plugs N9Y equivalent and just use car on street, not tracked. Hard to find high octane gas here without ethanol. (91 without ethanol, 94 with ethanol)
* plug checking over short duration runs may not be a reliable indicator

[TBG]

Hugely grateful for all the most helpful replies - I think I am getting there, though why just changing the head would make such a difference is beyond me - not difficult I have to admit. Thanks a bunch chaps. D

[webbslinger]

I want to correct my previous post. I am currently running 130 mains, not 135s.

[webbslinger]

This is the third time I will try to correct my earlier post to this thread. I checked and my carbs are using 130 mains, not 135s. Also, 33mm chokes and 27.5 mm fuel height which was the result for setting 151s per Webers plastic float instructions.

[ceejay]

For what its worth - The following set up below is what I have on my 1700cc Twin Cam engine build. (Dyno'd at 169BHP).
It is well worth the time and money putting the car on the rolling road dyno to find the sweet spot with the weber carbs... I'm very happy with the performance of the S2 elan.

I live three hours from a major Victorian city (Australia) but found a guy not 30 mins from where I live in another small town with the rolling road dyno, and he was also familiar with weber set up.

I initially machined/installed a set of 34mm chokes, but we couldn't get the carbs to work properly with them... so I finally refitted the 33mm chokes, and we soon found the sweet spot right through the rev range.

The following settings may/ may not work with another engine, as there are a host of different factors to take into account when fine tuning webers... but the rolling road is where the best results will be found.
Twin Cam Lotus 1700cc Engine.
Twin Weber DCOE 40mm Carb set up data.
Chokes: 33mm.
Main Jets: 125.
Emulsion Tubes: F2.
Air Correctors: 130.
Idle Jets: 40 F11.
Brass Floats-settings: 8.5 and 15mm.
Ram Tubes Length: 58mm (Custom Length).
Camshafts: Short Duration - 440” lift.
Inlet valve head Dia - 41.3mm.
Exhaust Valve Head Dia - 35.5mm
(Valve train - Rally pack
springs/titanium retainers - Tony Ingram)

This is the second twink engine build over forty years of elan ownership. The journey down the path of 1700cc twin cam building was a fantastic and deeper learning experience than just building a stock twin cam, and I was ever so thankful to able to bounce ideas and theories off Rohan when required, and also his generosity with some loan parts.
And pleased to say, now with about 3000KMs on the engine, it really performs and puts a huge grin on my face with every drive.
The gearbox is an ultra close (Legacy of its race car life (70s/80s) and we run a 3.55 Diff which I find to be a great combination.

One small issue that has developed recently with the gearbox is the loss of synchro on third gear, but as any sporting driver will know, its a just a simple matter of double clutching with a blip in the middle of the change and its as smooth as silk... but in the near future the engine and gearbox will be removed to carry out the gearbox rebuild, its all part and parcel of Lotus ownership, and there's not a split pin, nut or washer that I don't know on that car.

[TBG]

Ceejay - that is fascinating and it seems that I may have been barking up the wrong tree. My setup is as follows.

Chokes 34mm
Mains 150
AC 200
Immulsion tubes F16
Idle jets F8 40

Cams QED 420s
QED 55 valve springs
New QED big valve big port head

I reckon I may be getting about 135 hp judging from the rolling road, but it still has hesitance at low rpm and a bit of rough running higher up. I wish I had Rohan on my doorstep! Any ideas as to where I am going wrong CJ and Rohan? D

[mbell]

Ceejay - that is fascinating and it seems that I may have been barking up the wrong tree.

I've been going a different direct also, bigger idle jets, smaller mains with increase fuel level.

The general issue on twincams tend to be an off idle stumble and transition between circuits.

There also change in fuel (especially E10) that effect AFR and viscosity of the fuel a little. These likely result in needing a bit more fuel.

You can get the extra fuel from the idle circuit or the main circuit. On the idle circuit you go to bigger jet but with more air hole area to counter act the increase in fuel.

On the main circuit you have few options:
- Bigger main jet
- smaller air corrector
- Higher fuel level*
- smaller choke*

(* these also often make the main circuit work at lower rpms/loads)

I am at a 50 idle jet and 115 main (hypojets not std jets), 33mm chokes on a what I think is a standard-ish big valve engine. This runs and pulls across the range and loads well, on US E10 fuel. But it goes rich at high revs with throttle open or low revs high load with open throttle.That can likely be improved with leaning out the main circuit but I get a transition stumble if I do that. So to improve it I likely need to go up on the idle jets as well as down on the mains.

You seem to have the opposite set up to me, small idle jets and big mains. It sounds like you could be going lean at low rpms and over rich at high rpms. So I'd suggest trying bigger idle jets and smaller mains as a start.

[ceejay]

Ceejay - that is fascinating and it seems that I may have been barking up the wrong tree. My setup is as follows.

Chokes 34mm
Mains 150
AC 200
Immulsion tubes F16
Idle jets F8 40

Cams QED 420s
QED 55 valve springs
New QED big valve big port head

I reckon I may be getting about 135 hp judging from the rolling road, but it still has hesitance at low rpm and a bit of rough running higher up. I wish I had Rohan on my doorstep! Any ideas as to where I am going wrong CJ and Rohan? D

I rolled up at the dyno shop with webber settings that had been used for decades on the old 1600 twink, we did a couple of ramp tests to see what AFR carbs were delivering, (Plus a plug read) then using that info as the bench mark, the tuning/set up process began... the first dyno session got it close, but it took another visit to the dyno shop after installing the 33mm chokes to get it right, several hours were spent getting things right, cost was about AU$500.00, but worth every dollar.
Notes: The webers must be pristine inside, fuel bowl heights correct, Ign timing correct, valve clearances correct, etc etc,

[tonyabacus]

D
As already mentioned a visit to a rolling road is the best plan, because as you have experienced and from the responses so far, no two engines are the same. A good rolling road guy will sort it in no time and get the very best from your current configuration. Effectively having one carb for each cylinder means that any small deviation between the porting and chamber can be hard to spot without the rolling road.

I watched Roger at Aldons when he was setting up an Elan, his experience and the aid of the rolling road read outs soon had such variances sorted.
Tony

[David1953]

I took my S3 to JPR tuning just north of Bristol, and found it a most interesting day out, plus the fact the car has run very well ever since. They really know webers.

[TBG]

Hullo all you helpful people out there - especially Rohan and CJ. I have been struggling with jets these past weeks and at last seem to have got the sweet spot.

Mains 125
AC185
Idle F8 50
Keith Franks NF tubes.
Timing 13 degrees.

Running like a 6 cylinder - so smooth and tons of poke. Happy bunny!

Very happy if you have any comments to make.

[mbell]

Very happy if you have any comments to make.

Seemd to be much more inline with what I would have expected. Glad it's running well!

[ceejay]

Good to hear of another happy twink owner, its so nice to drive the elan with a sweet, well sorted twink, now go out and enjoy the drive.