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Weber Carburetor Jet Size

Fuel System

Vehicle Information: Model: 911T with engine rebuilt to S specification; Year: 1971; Body Type: Targa; Engine (type, size, modifications): 2.2 litre S with Pertronix / MSD Ignition; Total Mileage: 32,800;

The engine has been rebuilt to S specification. The fuel induction system has been changed to a dual Weber 40IDTP3C set-up. I have installed a Pertronix magnetic pick-up and Ignitor II coil and power the system with a MSD 6AL ignition through Magnecor competition wires. I am experiencing minor popping and backfiring when the engine is decelerating from high rev's, as well as when the engine is still cold. The carburetors are balanced, but the mixture adjustment screws seem unresponsive. I think the carburetors are probably dirty and that the jets may need replacing or changing to a different size. I'm pretty sure that these carburetors are original and have never been rebuilt. I plan to rebuild them this fall. What were the original, and the currently recommended, jet sizes? Do you know where I can get a complete jet set, instead of buying them individually? Do you also know a good source for an article, or instructions, on rebuilding Weber carburetors. I have the 101 Projects, and the Haynes book, but I don't think either of them provided good, set-by-step, instructions on how to do the job? With the new ignition system, should I still set the timing to 30 degrees BTDC? What spark plugs would you recommend for this engine.The biggest issue is that the power curve seems a little sluggish at low RPM, but it pulls well throughout the mid-range. After about 5,200 RPM, I also notice that the power seems to flatten out.This car is not an everyday driver, and I only drive it in the summer. I'm retired and I have lots of time to tinker with this car. I always used to do all of my own work, from tuning to complete engine rebuilds, when I was younger. I'm dedicated to the idea that this car will really 'haul ass' if its properly set-up and tuned. Thanks in advance for your assistance!

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