I've been troubleshooting an intermittent problem which relates to fuel supply. Whilst chasing the issue, I tuned in to a video posted by an illustrious ex-Fiat 500 owner who has now moved on to (amongst other cars) a Ferrari. In the course of sorting out the four (I think) massive Weber carbs which are fitted to the Ferrari engine, a real expert was enlisted to give advice. Amongst that advice was an observation that in the specific case being discussed, it was probably wise to increase the idle jet size slightly, due to modern, ethanol fuel containing less energy the the equivalent 100+ RON petrol which the car was designed to run on.
Back to my car; one of the symptoms is that the spark-plugs give me a rough idea that the engine is running a bit weak. So I looked at my carb,, which currently, is a 28IMB-1 on a 594 engine The idle jet is 0.45mm, and it bears signs of compression damage, possibly by being misaligned in its seat. Consequently it needs binning. I checked two of my later carbs, one being a 28IMB-12, and they are jetted with a 0.5mm. One of these jets also had damage to the bifurcations which secure it in its holder. Under the magnifying glass, that one also looks dodgy, so will also be binned. As in the Goldilocks story, the third one is just right, so I fitted it and went for a run.
I expected the mixture to need adjustment and it did. It was noticeable that I could get a deliberate, really slow and steady tickover before adustment. Being so slow, I was easily able to get the optimum point at which the engine ran smoothly. The mixture screw was about one and half turns out and now it's at just less than one and a quarter. After that there was an obvious point at which the idle screw achieved the best, normal tickover speed.
I will need to do some proper driving before I can be sure that this was a good move. As the idle jet is partly involved in fueling over quite a wide range of engine speeds, I suspect that it will affect performance and fuel consumption. The distorted jet may even have been the cause of my problems. But it maybe illustrates that a close inspection of these tiny components, which I have always taken for granted, does not go amiss.
Back to my car; one of the symptoms is that the spark-plugs give me a rough idea that the engine is running a bit weak. So I looked at my carb,, which currently, is a 28IMB-1 on a 594 engine The idle jet is 0.45mm, and it bears signs of compression damage, possibly by being misaligned in its seat. Consequently it needs binning. I checked two of my later carbs, one being a 28IMB-12, and they are jetted with a 0.5mm. One of these jets also had damage to the bifurcations which secure it in its holder. Under the magnifying glass, that one also looks dodgy, so will also be binned. As in the Goldilocks story, the third one is just right, so I fitted it and went for a run.
I expected the mixture to need adjustment and it did. It was noticeable that I could get a deliberate, really slow and steady tickover before adustment. Being so slow, I was easily able to get the optimum point at which the engine ran smoothly. The mixture screw was about one and half turns out and now it's at just less than one and a quarter. After that there was an obvious point at which the idle screw achieved the best, normal tickover speed.
I will need to do some proper driving before I can be sure that this was a good move. As the idle jet is partly involved in fueling over quite a wide range of engine speeds, I suspect that it will affect performance and fuel consumption. The distorted jet may even have been the cause of my problems. But it maybe illustrates that a close inspection of these tiny components, which I have always taken for granted, does not go amiss.
