Triple Weber settings

[Simonpfhc]

Hi all,

I’m rebuilding an Etype 4.2 engine that is running triple Webers. From discussions with the owner, it has never really run smoothly. I think it would benefit from time on a rolling road but am interested to get some feedback from owners who are running these carbs.

Would be useful to hear what jets and needle valves are being used??

It is a 4.2 with standard cams, XJ6 big valve head and tubular manifolds.

Thanks.

[bitsobrits]

I've run Webers on several different cars, (have them on 3 at the moment) but not on E types so can't help you with specifics there. But if Webers are unhappy, they most likely have not been properly jetted for the particular specification of the engine. Also, the advance curve will need optimized (generally speaking more initial advance with total advance remaining the same-i.e. a recurve of the distributor is required or something like a 123+ignition), and the manifolds need be working with the carbs, not against them.

On this last item, there is a popular manifold option out there for E-types with three tubes going into a wide fan shaped collector then into a single down pipe which is famous for causing a mid range flat spot (2000-2500 RPM). My conjecture, based on a simple flow test (mimicked the test I saw on ClassicFabs site), is that the fan shaped collector tends to cause reversion issues as opposed to the desirable scavenging effect of a more normal tightly grouped collector. No carbs like reversion pulses, but Webers seem to get especially cranky when this happens.

What I'm certain of is that changing the fan type collector manifolds out for a set of long tube manifolds with a proper collector (ClassicFabs) transformed my E type (running SU's) into a crisp, no flat spot revver without any other changes. Experience with Webers/Dellorto/Solex on Lotus TCs, Porsche, and most recently a Ferrari V-8 helped me to understand that unwisely chosen exhausts can impact the vacuum signal 'seen' by the carbs, requiring jetting changes and/or exhaust design or pipe diameter changes.

The engine being basically an air pump, anything you do to change the airflow through the 'system' will require changes to jets and air correctors when running Webers. Much more complicated than SU's in this regard. Personally I'm a big fan of the crisp throttle response and marvelous sound of properly set up Webers, and if you are willing to dive in and learn about setting them up they can be very rewarding, and not very expensive to get right. But if you are going to rely on a shop that is most likely not truly experienced in the intricacies of Weber idle/transition/main and starting circuits (and therefore bills many hours) I would suggest a conversion back to SU's for simplicity and cost management.

[abowie]

I have no experience with Webers on the XK engine. My advice would be to give the car to someone with a dyno who has a good reputation for knowing the Weber DCOE.

Here's some stuff I've collected over the years. No idea of its veracity.

1. There's a Mike Cassidy article https://www.dropbox.com/s/h8983mm6qxa3s ... E.pdf?dl=1 in the Knowledge base.

2. Weber carb setup recommended in the Haynes carb manual for s1.5 E Type:

Choke = 38
Venturi = 3.5
Emulsion Tube= F2
Main Jet = 1.65
Air Corrector Jet =1.90
Idle Jet = 0.65 F8
Accelerator PumpJet = 0.40
Accelerator Pump Inlet Valve with Exhaust Orifice = 0.50
Needle Valve =2.00

3. viewtopic.php?f=4&t=14449&start=20#p118049

4. Weber Wisdom in KB https://www.dropbox.com/s/7zhzctlaawjvq ... m.pdf?dl=1

5. and https://www.dropbox.com/s/4hj5d08yxoi0b ... r.pdf?dl=1

[Simonpfhc]

Thanks Andrew, great info

Thanks Steve, interesting info. I’m not a repair shop, but retired. I really enjoy working on these engines (rebuilt many) but haven’t worked with Webers for years and don’t really want to start playing with them now.

If I can simply improve them for the short time it takes to run in the engine before it goes to a rolling road, I will. All I plan to do is to replace the gaskets and clean out the jets. One of the cylinders has been running very lean and the rest look rich.

[44DHR]

Just to confirm, I have run triple Webers on my E Type for over 25 years and have done many miles including European trips such as down to Monaco and to Italy with them. They are Italian 45DCOE152 Webers, with 3 progression holes running through Pipercross foam socks sitting on 2.5 inch ram pipes. They have plastic floats set at 12mm. The engine breather runs down to an alloy catch tank under the Webers.
I run a stock SU electronic fuel pump and stock distributor but running Lumenition electronic ignition. I have a Hayward and Scott large bore stainless exhaust system including their headers.
The only difference to all the settings to those shown in Andrew’s post #3 is that I changed the main jets from the recommended 1.65 to 1.70. I did recently - last year - have a starting issue and misfire on idle which was resolved by fitting new inlet needle valves (size 200) as the original ones had worn a witness mark.






Hope this helps.
Cheers,
Dave

P.S. Edited at later date to confirm 3 Progression holes rather than 4 as originally stated.

[Simonpfhc]

Great feedback Dave, cheers.

[Paul bow]

Hi Simon.. I have run webbers on 2 of my previous e types, great carbs when set up and no better sound when flat out.
I don’t believe there’s a one size fits all in my experience and having spent many many hours adjusting and perfecting only to find that in reality I had simply moved that issue further forwards or backwards in the rpm range.
I can certainly recommend Northampton motorsport, their rolling road and experience is second to none, even at this time of the year you’ll prob wait at least 4 weeks for a slot, so many are after their services on the rollers.
I’ve wasted money with other so called Webber experts this is the only one I trust, came recommended to me from others on here..
good luck

[Simonpfhc]

Hi Paul,

Sounds like the perfect place! I’ve serviced the carbs and am just starting the engine rebuild. Should be finished in a couple of weeks. When the engine is fully run-in, I’ll encourage the owner to head there!

Cheers.