If you go back to the Webers to sort them out then I suggest you fit an air fuel gauge so you can see exactly what is going on. Anything else is guesswork. The AEM one works well but there are others. Weld a bung into the exhaust as far back as possible. As you have the original GTD non crossover exhaust it is probably a good idea to weld a bung into each side so you can swap the oxygen sensor over to check side to side. The two wires from the sensor go to the gauge. The gauge needs Positive and negative supply and you are good to go. You get real time readout of A/F ratio as you drive along and can check in a wide range of situations.
Here is some info that I put together for a NW member but it may be useful generally.
Are the float/fuel levels correct? Are the carb airflows in sync? Is the timing set correctly? Are the collectors sealed and not dragging air in?
To work out what is going on work through this process.
Sort out idle mixture with idle jets and holders so the mixture is around 14:1 and the engine runs smoothly.
You now need to drive the car watching the meter. The next stage of the carbs is the transition phase. The mixture is set by the tiny holes drilled just above the throttle plate. To see what is happening the throttle must be opened very slowly and carefully. If it is done fast the pump jets will squirt fuel in and mask everything. What is happening to A/F ratio as the throttle is very slowly opened? This tells you the transition mixture. This mixture is fed from the same circuit as the idle so they are to some extent interrelated.
As you open the throttle past the transition point the main jet comes into play. Continue to steadily open the throttle to fully open and note the A/F ratio. This will tell you if the main jet is correct.
The main jet assembly is in 3 parts. The emulsion tube, the main jet and the air corrector.
How it works is this - the main jet at the bottom lets in fuel from the float chamber and this sets the fuel level in the emulsion tube well. The bigger the main jet the more fuel is drawn up the emulsion tube well and the richer the mixture.
Air is drawn in through the air corrector at the top which mixes with the fuel to give what they call an emulsion ( more like a fuel air bubble mixture).. The bigger the air corrector the more air is drawn in which weakens the mixture. There are lots of little holes at various places on the emulsion tube so the mixture of air and fuel will vary as more fuel and air is drawn in by the vacuum from the inlet manifold. Different emulsion tubes have different hole patterns and this is what controls the fuel slope. This gives either a steady increase in A/F , a decreasing A/F or an increasing A/F. The numbers are F numbers but they are not in any kind of number order. As every engine is different the demand for fuel mixture may go up or down and this is what the emulsion tube does.
Next is what happens when you suddenly open the throttle. The engine takes in a gulp of air and the fuel from the main jet can't react quickly enough so it goes lean and the engine bogs and stutters. To compensate for tis the carb has a pump jet. This shoots in a jet of fuel. The size and duration of this squirt is set by a pump which sends fuel into the carb opening.- the size of the squirt is set by the pump jet - the bigger the pump jet the bigger the squirt. Not all the fuel goes into the intake as there is a return jet which leaks some of it back to the float chamber. So the bigger the return jet the less fuel in the squirt and also the quicker the pressure from the pump drops so this controls the length of time of the squirt.
It is important when looking at the A/F to separate the idle, transition and main jet running by not bringing in the pump jet by opening the throttle too fast as this will operate the pump jet. Check the pump jet by looking at happens when you stab the throttle open. Does it go rich or lean? Does the squirt last long enough or is it too brief. Is the mixture correct enough to prevent the engine bogging down through going too rich or too lean.
Then in something like 3rd gear hit the throttle hard and watch the gauge A/F . Does it go instantly lean or rich? Does it keep a good a/F until the main jets come in and catch up to the sudden throttle opening.
Video of emulsion tube in action.
Hope this makes sense
Cheers
Mike
