4.2 3x45 Webber’s running 12 deg advance?

[frank77]

Yes, it is aftermarket: 2“ short tube 3 into 1 stainless steel headers. Engine is mildly tuned with larger valves, Rob Beere fast road cam, forged pistons etc. Maximum power is not an issue

It is more like a little hickup at 1500.
When I move the pedal rather gentil until I am over 1500, then it is fine.

During cruising on normal streets around 2000-2500, it then is to fat. Lambda readings are around 10-11.
Throttle is almost closed, so the Webers are still running on the idle circuit + some of the prog. holes.
But when I make it leaner here to 12-13 and accelerate, lambda goes to 14-16 and the car stalls. Already tried 55F8, 60F4, 60F14.
So I kept the 60F8 with a cruising setup a little to fat, but it works.
Thought the 5 holes might help here.

This is my actual setting:
Idle jet 60F8
Main jet 140
Air correction 180
Emulsion tube F7
Choke 36mm
Auxiliary venturi 4.5
Pump jet 45
Pump spill 40

[Paul bow]

Frank .. I had exactly the same problem with 5 hole webbers, spent the same on a rolling road and nothing but frustration.
Always popping and banging on the over run, however went like a scalded cat with zero hesitation..
I don’t have the answer but I could recommend you speak with Northampton motorsport imo they are without a doubt one of the best rolling roads Troy has a wealth of knowledge they on average do 2/3 sessions 5 days a week and are booked up months in advance.

[Rich70]

Choke 32, mains 1.45, f16 tubes, air correction 220.

Paul,

Do you have the Dyno printout? Ideally with the Air Fuel Ratio (AFR) overlay - always ask for this after a Dyno run.
I would suggest that the choke is far too small. Your 32mm choke will cause a significantly richer running from the 145MJ that you have. The air correction jet is also very large, probably trying to compensate for the richness induced by the choke.

I would advise 36mm chokes with a 3.5 Aux venturi. Keep your 145 MJ and drop the AJ to circa 190. An F2 tube is more common, but the F16s make sense with such a small choke. Then the idle jets need to be revised- lots of options! I'm guessing a professional garage will charge circa £100p/h to change these items and at least 30 mins a carb.

Also, I have 123 Tune Bluetooth. It's superb and well worth the investment!

A small choke will get you off the line quickly and give you good low-down torque, and the feeling of a fast 'scalded cat' launch, but you will probably lack power as the revs rise.

You need to see what the AFR is doing here.

Good luck at Northampton MS!

Rich

[frank77]

Hi all,
Did some more testing on my setup. To compare each test drive I installed a small endoscope camera on carb 1 and made small markings on the outside of carb 2 when each of the progression holes is opened. So while driving I could exactly see in the endoscope display where the throttle position is.
Almost all of the normal cruising is done in this progression area.





Here are the AFR readings with different setups and my very subjective comments:


With the green and blue setup I went on a rolling road and optimized the main jet, air correction jet and also the 123 ignition curve a bit, I stayed with the green setup.

Rolling road chart:


And this is the 123 curve:


Maybe this helps someone, I learned a lot.
Engine gained some 10 hp (260 DIN hp) and fuel consumption went down about 1-2 l/100 km

Cheers
Frank