You are lucky enough to have something like an MG MGB. Carefully maintained, you will suddenly notice that the engine will run a little harder under the slightest acceleration, even sputtering. Add the workshop manual and adjust it a little more richly? Not handy, because then the engine runs idle too rich ... Is not good for fuel consumption - and therefore your wallet -, but also not for the environment.
At the factory, when your MG was still new, the engine was tuned so economically that it ran perfectly. Also when accelerating. Decades and so many tens of thousands of kilometers further, things are a bit worn down, let's say worn out. And then a connoisseur (...) also informed you that the standard fitted air filters were replaced by those of K&N. “Gives better breathing, a nicer suction sound and it picks up better” exclaimed the enthusiast. He forgot to tell you that you also had to replace the needles of the SU carburettors. These must then - in principle - be of the AAA type. You are not there yet, because you then have to experiment a bit, whereby we note that it might be wise to check the website www.mintylamb.co.uk/suneedle/ to consult. That saves you a lot of time. The engine in your MG is of the type 18V847 and should be equipped with ACD needles depending on the year of manufacture. Early 18V engines have AAU needles. They were not so 'sharply' adjusted. For the sake of clarity, whichever needles you go for, they must be adjusted. If the engine is running at a perfect idle speed, there will be less pulling power at higher speeds. If it runs richer at the bottom, it will continue to perform perfectly at the top. The decision is yours. If you consider going to a dynamometer, always ask first whether the wheels between the roles are, because only such a dynamometer offers perspective!