So it's way too rich at idle and fouling the plugs..
Obviously way out of my league but could they have also done all kinds of weird and wonderful things with the jetting etc too ?
1. Yes.
2. Your popping with the other cam may have been due to your wasted distributor gear, however, it was most likely partially caused by the plugs loading up . As I mentioned a few times, it is missing and popping now because the plugs are loading up . That is why it ran fine again for a few minutes after you cleaned them . I can guarantee you that your carbs were rich on top end with the previous camshaft if the plugs looked like that.
3. Please don't ask how a carburetor works, especially a weber . It will be impossible to understand and pointless . A weber is a fkn nightmare and can take a rocket scientist hours to tune on a dyno . A holley can be tuned in 15 minutes without a dyno by any moron on the planet. 99.9% of the people that have webers on a street car that think they are perfectly tuned are wrong . For a weber to work really well on a street car, it needs a a lot of vacuum . The way to get a lot of vacuum is to put in a tiny camshaft, and in fact, a stock camshaft is the best choice for a weber, however, using a stock camshaft with a set of $4000.00 racing carburetors kind of defeats the purpose.
When you see webers on a true racing engine, the engine will be idling at over 1500 rpm and sometimes more . To even begin to understand how to tune a weber PROPERLY, you must FULLY understand how an emulsion tube works, whereas this is not necessary to understand on a holley . Below is just a very short explanation about how they work.
http://www.hotrod.com/how-to/engine/0611phr-the-secret-life-of-carburetors/"The calibration components considered so far have been the main jet, the emulsion tube, and the air bleed. Starting at the main jet, we find that a larger main jet makes the mixture richer, and vice versa. The effect of the emulsion tube will depend on the hole pattern. Here is how to read it: First, hold the emulsion tube upside down and inspect the hole pattern. Holes at the top of the emulsion tube will affect the top-end of the rev range. Holes in the middle will trim the mid-rpm range, and holes at the bottom, the low-rpm range. Where there are no holes, the mixture will be rich. Where there are holes, the mixture will be leaned out. Just how much the mixture is leaned out by the presence of holes depends on how many, and how big. The more holes present, the more the mixture is leaned out at that point. Because it is fed with air from the air bleeds, the emulsion tube's overall function is influenced by the air bleed size. A larger air bleed leans out the mixture, but at low rpm and small throttle openings, the air bleed has little influence over the mixture. As the engine's demand for air increases due to an increase in throttle opening and rpm, so the air bleed's influence increases. At high rpm, just a few thousandths change in the air bleed diameter can have a significant effect on mixture.
One other aspect of the emulsion tube and well is that they act not only as a means of calibration but also as a control element for fuel atomization. By emulsifying the fuel prior to it reaching the booster, the fuel is easier to shear into fine droplets at the point of discharge. Generally, the more it is emulsified with air in the emulsion tube, the easier it is to atomize at the venturi. With an understanding of how it is achieved, let us now look at what we need the main circuit to deliver in the way of air-to-fuel ratio."
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