Interesting Weber jetting

[Eljaro]

I have been fine tuning my webers, especially trying to lean out the whole thing, because it was smelling too much of gas and using a lot of it..
Large main jets and idel jets are fine and make things run, because they mask any other deficiencies in the choice of air jets.
I went to smaller jets , 55 idle and 145 main and worked myself up from there.
At idle the A/F ratio came down to 13.5 on idle, but went very lean when starting to move.
So I removed the 120 idle air jet and went to a 100, which improved things a lot. I subsequently installed a self made 80 ( drilled out a 60 idle holder) idle holder air and things got in line quite well.
I noticed a slight lean hole when accelerating, so decided to open the pump Jets up from 50 to 60.Good result.
The main jets at 145 were a little too rich and power and acceleration was slightly hampered, at 13.5 to 14 A/F ratio. Since I wanted to achieve a A/F ratio of 12.8, which is for maximum power I installed a 155 main jet. The air jet is 120 and maintains the 12.8 ratio up to max rev , that is 6200 rpm.
The whole thing is slightly on the rich side, but I just thing that it has to be like that to make these engines run to its best.
Definitely Webers give these engines the crisp and inmediate response other carburetors don’t. I always had problems with Holleys sputtering when taking fast corners or when breaking hard (killing the engine in the process). Whit the Webers this is now an absolute race engine, with incredible torque and reving capabilities ( I have an aluminum flywheel) and a sound to make you absolutely happy.

I have a friend who is a Rally champion here in the Balearics( with Ford Cosworths and the like), and who had a chance to drive in McLaren F1 and several top Ferrari models. He said that the sensation of brute power and of blood draining acceleration he had in my Cobra topped anything he had driven before.

If you snap the gas pedal open from 1500-2000 rpm , first you go sideways, the back trying to overtake the front by the right side. You correct for that and there you go off like a rocket.
Fantastic sensation. You better have some good driving experience doing that or you can destroy yourself.

Anyway, my concept of supercars has changed a lot. For sheer fun I only need my Weber equipped Cobra, nothing else.

[dallas_]

Good update. Sounds like you got it dialed in pretty good!

Can you elaborate on your setup to read your A/F ratio's?

[Eljaro]

I have a wideband Lambda sensor with a bung installed in the left exhaust pipe, where the four headers meet the exhaust. An Innovative LM-2 A/F ratio meter gives me the readings. I read the A/F ratios while driving the car.

[Eljaro]

As you probably know from my other thread my Weber experiments have come to a sudden halt.
The crankshaft could not bear the enormous torsion forces of the snap action acceleration combined with a light flywheel. It broke in half and exploded part of the block.
Yes, the eagle crankshaft has broken just before the second bearing cap at the front and has taken the Pond aluminum block with it, so the engine is now for a general rebuild, well , rather a general replacement.
Will probably go with a new but cast iron block and will try to get a better crankshaft, forged or billet. The steel eagle crankshafts seem to break elswhere also, I have seen other broken ones in the web.
So I am very sad, but one thing can positively be said about the Webers. They made my engine behave at its best. My last settings were probably the best ones I managed to achieve. Can't wait to have the engine back together and enjoy the brutal response the Webers transmit.