In general, looking to get about 50 - 55% of calories from carbs is a realistic goal for most folks. The math is pretty easy because a gram of carbs contains 4 calories. So for a 1,600 calorie diet that would be about 220 grams per day. (1600 x 0.55) / 4 = 220.
Brake boosters are used only on power brakes, not manual brakes. The booster's function is to give more braking power with minimal pressure on the brake pedal. If the booster is not working properly, you will still have brakes, but the brake pedal will be very hard to push. A brake booster is what gives power brakes their power. It works on vacuum from the engine. The booster pushes on the master cylinder with the pressure applied to the booster by stepping on the brake. If the engine is off, it cannot get vacuum, therefore the brakes will be hard when the engine is off.
No. The booster will never cause a low or soft brake pedal, check for air or other hydraulic problems. A defective booster will only cause the pedal to become hard or not return. Check the vacuum source to the booster. Not only does the booster need at least 15 in. Hg, it also needs vacuum volume. The fitting normally on the intake manifold or carburetor will get clogged with carbon build up and restrict the vacuum volume.